On behalf of the board of directors of First Citizens Bancshares, Inc. (“First Citizens”), we are pleased to enclose the accompanying proxy statement/prospectus relating to the proposed merger of First Citizens with and into Park National Corporation (“Park”). We are requesting that you take certain actions as a holder of First Citizens voting common stock or First Citizens Class A common stock (collectively, “First Citizens common stock”).

The boards of directors of Park and First Citizens have each unanimously approved an Agreement and Plan of Merger, dated as of October 27, 2025, by and between Park and First Citizens (as amended from time to time, the “merger agreement”). Pursuant to the merger agreement, First Citizens will merge with and into Park (the “merger”), with Park as the surviving corporation (the “surviving corporation” or “Park”, as the case may be). Immediately following the merger, First Citizens National Bank, a national banking association and a wholly-owned subsidiary of First Citizens (“First Citizens National Bank”), will merge with and into The Park National Bank, a national banking association and a wholly-owned subsidiary of Park (“Park National Bank”), with Park National Bank as the surviving bank (the “bank merger”).

At the effective time of the merger, holders of First Citizens common stock will receive 0.52 of a share (the “exchange ratio” and such shares, the “merger consideration”) of Park common stock for each share of First Citizens common stock they own. Based on the $157.31 per share closing price of Park common stock on the NYSE American stock exchange (the “NYSE American”) on October 27, 2025, the last trading day before public announcement of the merger, the exchange ratio represented approximately $81.80 in value for each share of First Citizens common stock. Based on the $163.81 per share closing price of Park common stock on the NYSE American on December 11, 2025, the last practicable trading day before the date of the accompanying proxy statement/prospectus, the exchange ratio represented approximately $85.18 in value for each share of First Citizens common stock. The value of Park common stock at the time of completion of the merger could be greater than, less than or the same as the value of Park common stock on the date of the accompanying proxy statement/prospectus. We urge you to obtain current market quotations of Park common stock, which is listed on the NYSE American under the trading symbol “PRK”.

We expect the merger will qualify as a “reorganization” for U.S. federal income tax purposes. Accordingly, U.S. holders of First Citizens common stock generally will not recognize any gain or loss for federal income tax purposes on the exchange of shares of First Citizens common stock for shares of Park common stock in the merger, except with respect to any cash received in lieu of fractional shares of Park common stock. For more information regarding the tax consequences in the merger, see the section entitled “Material U.S. Federal Income Tax Consequences of the Merger.”

Based on the number of shares of First Citizens common stock outstanding and reserved for issuance as of December 11, 2025, Park expects to issue approximately 1.99 million shares of Park common stock to holders of First Citizens common stock in the aggregate in the merger. Following the completion of the merger, we estimate that former holders of First Citizens common stock will collectively own approximately 11% and existing holders of Park common stock as of the record date will own approximately 89% of the common stock of the surviving corporation.

First Citizens will hold a special meeting of its shareholders in connection with the merger. At the First Citizens special meeting, holders of First Citizens voting common stock and holders of First Citizens Class A common stock, voting separately, will be asked to consider and vote on (i) a proposal to approve the merger agreement (the “First Citizens merger proposal”) and (ii) a proposal to adjourn or postpone the First Citizens special meeting, if necessary or appropriate, to solicit additional proxies if, immediately prior to such adjournment or postponement, there are insufficient votes to approve the First Citizens merger proposal or to ensure that any supplement or amendment to the accompanying proxy statement/prospectus is timely provided to the holders of First Citizens common stock (the “First Citizens adjournment proposal”). Park and First Citizens cannot complete the merger unless the holders of First Citizens voting common stock and the holders of First Citizens Class A common stock, voting separately as two classes, approve the First Citizens merger proposal. The First Citizens board of directors (the “First Citizens board of directors”) is providing this proxy statement/prospectus to solicit First Citizens shareholders’ proxy to vote in connection with the First Citizens merger proposal and the First Citizens adjournment proposal. This document is also a prospectus that is being delivered to holders of First Citizens common stock because, in connection with the merger, Park is offering shares of Park common stock to the holders of First Citizens common stock.

The First Citizens special meeting will be held virtually via the Internet, on Wednesday, January 21, 2026, at 10:00 a.m., Central Time. You will be able to attend the First Citizens special meeting by visiting http://www.virtualshareholdermeeting.com/FIZN2026SM (the “First Citizens special meeting website”) and using the 16-digit control number included in your proxy card. Additional information about the First Citizens special meeting and the merger is contained in this proxy statement/prospectus. In particular, see “Risk Factors” beginning on page 16. We urge you to read this proxy statement/prospectus carefully and in its entirety.

Whether or not you plan to attend the First Citizens special meeting, please vote as soon as possible to make sure that your shares are represented at the meeting. If you do not vote, it will have the same effect as voting “AGAINST” the merger. The First Citizens board of directors unanimously recommends that holders of First Citizens common stock vote “FOR” each of the proposals to be considered at the First Citizens special meeting. We strongly support this combination of First Citizens and Park and recommend that you vote in favor of the approval of the First Citizens merger proposal.

Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved the merger, including the issuance of the securities to be issued under this proxy statement/prospectus, or determined if this proxy statement/prospectus is accurate or adequate. Any representation to the contrary is a criminal offense. The securities that Park is offering through this document are not savings or deposit accounts or other obligations of any bank or nonbank subsidiary of Park or First Citizens, and they are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

This proxy statement/prospectus is dated [  ] [ ], 2025, and it is first being mailed or otherwise delivered to First Citizens shareholders on or about [   ] [  ], 2025.

This proxy statement/prospectus incorporates important business and financial information about Park from documents filed with the SEC that have not been included in or delivered with this document.

This information is described on page 137 under “Where You Can Find More Information.” You can obtain free copies of this information by writing or calling:

You will not be charged for any of these documents that you request. To obtain timely delivery of these documents, you must request them by January 7, 2026, in order to receive them before the First Citizens special meeting.

No one has been authorized to provide you with information that is different from that contained in, or incorporated by reference into, this proxy statement/prospectus. This proxy statement/prospectus is dated [   ], and you should assume that the information in this document is accurate only as of such date. You should assume that the information incorporated by reference into this document is accurate as of the date of such incorporated document. Neither the mailing of this proxy statement/prospectus to First Citizens shareholders nor the issuance by Park of shares of Park common stock in connection with the merger will create any implication to the contrary.

This proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction to or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction. Except where the context otherwise indicates, information contained in, or incorporated by reference into, this document regarding First Citizens has been provided by First Citizens and information contained in, or incorporated by reference into, this document regarding Park has been provided by Park.

See the section entitled “Where You Can Find More Information” beginning on page 137 of this proxy statement/prospectus for further information.

On October 27, 2025, First Citizens Bancshares, Inc. (“First Citizens”) and Park National Corporation (“Park”) entered into an Agreement and Plan of Merger (as amended from time to time, the “merger agreement”), a copy of which is attached as Annex A to the accompanying proxy statement/prospectus to which this notice is a part, pursuant to which First Citizens will merge with and into Park (the “merger”).

NOTICE IS HEREBY GIVEN that a special meeting (the “First Citizens special meeting”) of holders of First Citizens voting common stock and First Citizens Class A common stock (collectively, the “First Citizens common stock”) will be held virtually on Wednesday, January 21, 2026, at 10:00 a.m., Central Time (unless it is adjourned or postponed to a later date). The First Citizens special meeting will be held exclusively online via webcast. You will be able to attend the First Citizens special meeting by visiting www.virtualshareholdermeeting.com/FIZN2026SM (the “First Citizens special meeting website”) and using the 16-digit control number included in your proxy card or the voting instruction form provided by your bank, broker, trustee, nominee or other holder of record if you hold your shares of First Citizens common stock in “street name” (including through the First Citizens National Bank Employee Stock Ownership Plan and Trust). You will be able to vote your shares electronically over the Internet during the meeting by logging in to the First Citizens special meeting website and using the control number.

At the First Citizens special meeting, the holders of First Citizens voting common stock and holders of First Citizens Class A common stock, voting as separate classes, will be asked to consider and vote on the following matters:

The First Citizens board of directors has fixed the close of business on November 19, 2025 as the record date for the First Citizens special meeting. Only holders of record of First Citizens voting common stock as of the close of business on the record date for the First Citizens special meeting are entitled to notice of, and to vote at, the First Citizens special meeting or any adjournment or postponement thereof.

The First Citizens board of directors unanimously recommends that holders of First Citizens voting common stock and holders of First Citizens Class A common stock vote “FOR” the First Citizens merger proposal and “FOR” the First Citizens adjournment proposal.

First Citizens will transact no other business at the First Citizens special meeting, except for business properly brought before the First Citizens special meeting or any adjournments or postponements thereof by or at the direction of the First Citizens board of directors.

First Citizens has concluded that its shareholders are entitled to assert dissenters’ rights to the First Citizens merger proposal. A First Citizen shareholder’s dissenters’ rights are conditioned on such holder’s strict compliance with the requirements of Chapter 23 of Title 48 of the Tennessee Business Corporation Act (the “TBCA”). A copy of the applicable statutory provisions of the TBCA is included as Annex D to the accompanying proxy statement/prospectus and a summary of these provisions can be found under the caption “The Merger — Appraisal or Dissenters’ Rights in the Merger” beginning on page 68.

Your vote is important, regardless of the number of shares you own. We cannot complete the transactions contemplated by the merger agreement unless the holders of First Citizens voting common stock and holders of First Citizens Class A common stock separately approve the First Citizens merger proposal. The affirmative vote of the holders of at least a majority of the outstanding shares of the First Citizens voting common stock and the affirmative vote of the holders of at least a majority of the outstanding shares of the First Citizens Class A common stock, voting as separate classes, either in person (virtually) or by proxy at the First Citizens special meeting is required to approve the First Citizens merger proposal.

Each copy of the proxy statement/prospectus mailed to First Citizens shareholders is accompanied by a form of proxy with instructions for voting your shares of First Citizens voting common stock or First Citizens Class A common stock. Whether or not you plan to attend the First Citizens special meeting, we urge you to please promptly complete, sign, date and return the accompanying proxy card in the enclosed postage-paid envelope or authorize the individuals named on the accompanying proxy card to vote your shares by calling the toll-free telephone number or by using the Internet as described in the instructions included with the accompanying proxy card. If your shares are held in the name of a bank, broker, trustee (including through the First Citizens National Bank Employee Stock Ownership Plan and Trust) or other nominee, please follow the instructions on the voting instruction card furnished by such bank, broker, trustee or other nominee.

The proxy statement/prospectus of which this notice is a part provides a detailed description of the merger agreement, the transactions contemplated thereby, including the merger, and the other matters to be considered at the First Citizens special meeting. A summary of the merger agreement is included in the proxy statement/prospectus in the sections entitled “The Merger” and “The Merger Agreement”, and a copy of the merger agreement is attached as Annex A to the proxy statement prospectus, each of which are incorporated by reference into this notice to the same extent as if fully set forth herein. We encourage you to carefully read this proxy statement/prospectus (including the annexes thereto) and any other documents incorporated by reference herein in their entirety.

If you have any questions regarding the accompanying proxy statement/prospectus or need assistance with voting, you may contact Campaign Management LLC, First Citizens’ proxy solicitor, by calling toll free at (844) 410-4009, or by e-mail at info@campaign-mgmt.com.

Certain abbreviations and terms used in the text and notes of this proxy statement/prospectus are defined below:

The following are some questions that you may have about the merger and the First Citizens special meeting, and brief answers to those questions. You are urged to read carefully the remainder of this proxy statement/ prospectus because the information in this section does not provide all of the information that might be important to you with respect to the merger and the First Citizens special meeting. Additional important information is also contained in the documents incorporated by reference into this proxy statement/prospectus. See the section entitled “Where You Can Find More Information” beginning on page 137.

An investment by First Citizens shareholders in Park common stock as a result of the exchange of shares of First Citizens common stock for shares of Park common stock in the merger involves certain risks. Certain material risks and uncertainties connected with the merger agreement and transactions contemplated thereby, including the merger and bank merger and ownership of Park common stock, are discussed below. In addition, Park discusses certain other material risks connected with the ownership of Park common stock and with Park’s business under the caption entitled “Risk Factors” appearing in its Annual Report on Form 10-K most recently filed with the SEC and may include additional or updated disclosures of such material risks in its subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K that Park has filed with the SEC or may file with the SEC after the date of this proxy statement/prospectus, each of which reports is or will be incorporated by reference in this proxy statement/prospectus.

First Citizens shareholders should carefully read and consider all of these risks and all other information contained in or incorporated by reference into this proxy statement/prospectus, including the discussions of risk factors included in the documents incorporated by reference in this proxy statement/prospectus, in deciding whether to vote for approval of the various proposals for which they may be entitled to vote at the First Citizens special meeting described herein. The risks described in this proxy statement/prospectus and in those documents incorporated by reference (i) may adversely affect the value of Park common stock that you, as an existing First Citizens shareholder, will hold upon consummation of the merger, and (ii) could result in a significant decline in the value of Park common stock and cause the First Citizens shareholders to lose all or part of the value of their investments in Park common stock.

In connection with the merger, each share of First Citizens common stock issued and outstanding immediately prior to the effective time of the merger (excluding dissenting shares, treasury shares and shares owned by First Citizens or Park (other than the exception shares)) will be converted into the right to receive 0.52 of a share of Park common stock. The market value of Park common stock will fluctuate, and any changes in the price of Park common stock prior to the effective time of the merger will affect the value that holders of First Citizens common stock will receive in the merger.

Stock price changes may result from a variety of factors, including, but not limited to, general market and economic conditions, changes in Park’s and First Citizens’ businesses, operations, financial performance or prospects, volatility in the prices of securities in global financial markets, regulatory considerations, and tax laws, many of which factors are beyond Park’s or First Citizens’ control. Therefore, at the time of the First Citizens special meeting, First Citizens shareholders will not know the market value of the merger consideration to be received at the effective time. You should obtain current market quotations for shares of Park common stock (NYSE American: PRK).

Upon completion of the merger, First Citizens shareholders will become Park shareholders. Park’s business differs from that of First Citizens, and, accordingly, the results of operations of Park and the market price of Park common stock after the completion of the merger may be affected by factors different from those currently affecting the independent results of operations of each of Park and First Citizens. For a discussion of the businesses of Park and First Citizens and certain factors to consider in connection with those businesses, see the documents incorporated by reference in this proxy statement/prospectus and referred to under “Where You Can Find More Information” beginning on page 137, and the sections entitled “Information About Park” beginning on page 42, “Information About First Citizens” beginning on page 43 and “Business of First Citizens” beginning on page 93.

The unaudited pro forma condensed combined financial information in this proxy statement/prospectus is presented for illustrative purposes only and is not necessarily indicative of what Park’s actual financial condition or results of operations would have been had the merger been completed on the dates indicated. The unaudited pro

forma condensed combined financial information reflects adjustments, which are based upon preliminary estimates, to record First Citizens’ identifiable assets acquired and liabilities assumed at fair value and the resulting goodwill recognized. The fair value estimates reflected in this proxy statement/prospectus are preliminary, and the final amounts will be based upon the actual consideration paid and the fair value of the assets and liabilities of First Citizens as of the closing date. Accordingly, (i) the actual value of the consideration paid and the fair value of such assets and liabilities may vary significantly from the value used in preparing the unaudited pro forma condensed combined financial information in this proxy statement/prospectus, and (ii) the final acquisition accounting adjustments may differ materially from the pro forma adjustments reflected in this proxy statement/prospectus.

Each of First Citizens and Park has incurred and expects to incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the merger agreement. These costs include legal, financial advisory, accounting, consulting and other advisory fees, severance/employee benefit-related costs, filing fees and other regulatory fees, financial and other printing costs, and other related costs. Some of these costs are payable by either First Citizens or Park regardless of whether the merger is completed. If the merger is not completed, First Citizens and Park would have to recognize these expenses without realizing the expected benefits of the merger. See “The Merger Agreement — Fees and Expenses” beginning on page 87.

In addition, the surviving corporation will incur integration costs following the completion of the merger as Park integrates First Citizens’ businesses with its existing businesses, including costs relating to facilities, systems, consolidation efforts, and workforce-related matters. The surviving corporation may also incur additional costs to maintain employee morale and to retain key employees. A large number of processes, policies, procedures, operations, technologies and systems may need to be integrated, including purchasing, accounting and finance, payroll, compliance, treasury management, branch operations, vendor management, risk management, lines of business, pricing and benefits. While Park and First Citizens have assumed that a certain level of costs will be incurred, there are many factors beyond their control that could affect the total amount or the timing of the integration costs. Moreover, many of the costs that will be incurred are, by their nature, difficult to estimate accurately. These integration costs may result in the surviving corporation taking charges against earnings following the completion of the merger, and the amount and timing of such charges are uncertain at this time. There can be no assurances that the expected benefits and efficiencies related to the integration of the businesses will be realized to offset these transactions and integration costs over time.

The success of the merger will depend, in part, on the ability to realize the anticipated cost savings from combining the businesses of Park and First Citizens. To realize the anticipated benefits and cost savings from the merger, Park and First Citizens must successfully integrate and combine their businesses in a manner that permits those cost savings to be realized. If Park and First Citizens are not able to successfully achieve these objectives, the anticipated benefits of the merger may not be realized fully or at all, or may take longer to realize than expected. In addition, the actual cost savings and anticipated benefits of the merger could be less than anticipated, and integration may result in additional unforeseen expenses.

Park and First Citizens have operated and, until the completion of the merger, must continue to operate, independently. It is possible that the integration process could result in the loss of key employees, the disruption of each company’s ongoing business or inconsistencies in standards, controls, procedures and policies that adversely affect the companies’ ability to maintain relationships with clients, customers, depositors and employees or to achieve the anticipated benefits and cost savings of the merger. Integration efforts between the two companies may also divert management attention and resources. These integration matters could have an adverse effect on each of Park and First Citizens during this transition period and on Park for an undetermined period after the merger’s completion.

The success of the merger and the bank merger will depend in part on Park’s ability to retain the talents and dedication of key employees currently employed by First Citizens. Certain employees of First Citizens may decide not to remain with First Citizens while the merger is pending or with Park after the merger is completed. If key employees terminate their employment, or if an insufficient number of employees are retained to maintain effective operations, Park’s business activities may be adversely affected and management’s attention may be diverted from successfully integrating First Citizens to hiring suitable replacements, all of which may cause Park’s business to suffer. In addition, Park may be unable to locate suitable replacements or to offer such employment to potential replacements on reasonable terms.

Before the merger and the bank merger may be completed, various approvals, consents, waivers, and/or non-objections must be obtained from the Federal Reserve Board and the OCC. Other approvals, consents, waivers and non-objections from regulators could also be required. In determining whether to grant these approvals, the regulators consider a variety of factors, including the regulatory standing of each party and the factors described under “The Merger — Regulatory Approvals” beginning on page 66. These approvals could be delayed or not obtained at all, including due to any or all of the following: (i) an adverse development in any party’s regulatory standing or any other factors considered by regulators in granting such approvals; (ii) governmental, political or community group inquiries, investigations or opposition; or (iii) changes in legislation or the political environment.

The approvals that are granted may impose terms and conditions, limitations, obligations or costs, require branch divestitures or place restrictions on the conduct of Park’s business or require changes to the terms of the transactions contemplated by the merger agreement. There can be no assurance that regulators will not impose any such conditions, limitations, obligations or restrictions or that such conditions, limitations, obligations or restrictions will not have the effect of delaying the completion of any of the transactions contemplated by the merger agreement, imposing additional material costs on or materially limiting the revenues of Park following the merger or will otherwise reduce the anticipated benefits of the merger. In addition, there can be no assurance that any such conditions, limitations, obligations or restrictions will not result in the delay or abandonment of the merger. Additionally, the completion of the merger is conditioned on the absence of laws, statutes, rules, regulations, orders, injunctions or decrees enacted, entered, promulgated or enforced by any governmental entity of competent jurisdiction that would prohibit or make illegal the completion of any of the transactions contemplated by the merger agreement, including the merger and the bank merger.

Despite the parties’ commitments to use their reasonable best efforts to promptly prepare and file all necessary documentation in connection with regulatory approvals and cooperate with each other to respond to any request for information and resolve any objection that may be asserted by any governmental entity with respect to the merger agreement, neither Park, First Citizens, nor their respective subsidiaries is required under the terms of the merger agreement to take any action, or agree to take any action, or commit to take any action, or agree to any condition or restriction in connection with obtaining these approvals, that would, individually or in the aggregate, reasonably be likely to have a material adverse effect on the surviving corporation, taken as a whole and considered on a scale relative to First Citizens and its subsidiaries, after giving effect to the merger. For more information on the regulatory approvals required under the merger agreement, see the section entitled “The Merger — Regulatory Approvals” beginning on page 66.

Some of First Citizens’ directors and executive officers may have interests in the merger and have arrangements that are different from, or in addition to, those of First Citizens shareholders generally. Such interests include (i) the continuation by Park of certain benefits arrangements currently in place between First Citizens and certain of its directors and executive officers, (ii) Park National Bank entering into new employment agreements with executive officers of First Citizens, and (iii) the right to indemnification and insurance coverage for all of First Citizens’ directors and executive officers following the consummation of the merger. The First Citizens board of directors was aware of these interests and considered these interests, among other matters, when making its decision to approve

the merger and the merger agreement, and in recommending that First Citizens shareholders approve the First Citizens merger proposal. See the section entitled “The Merger — Interests of First Citizens’ Directors and Executive Officers in the Merger” beginning on page 60 for a more complete description of these interests.

If the merger is not completed for any reason, including as a result of First Citizens shareholders failing to approve the First Citizens merger proposal, there may be various adverse consequences. For example, Park’s or First Citizens’ businesses may have been impacted adversely by the failure to pursue other beneficial opportunities due to the focus of management on the merger, without realizing any of the anticipated benefits of completing the merger. Additionally, if the merger agreement is terminated, the market price of Park common stock could decline to the extent that the current market prices reflect a market assumption that the merger will be completed. If the merger agreement is terminated under certain circumstances, First Citizens may be required to pay a termination fee of $12.5 million to Park. See the section entitled “The Merger Agreement — Termination Fee” on page 87 for a complete discussion of the circumstances under which any such termination fee will be required to be paid.

Whether or not the merger is ultimately consummated, uncertainty about the effect of the merger on employees and customers may have an adverse effect on Park and First Citizens. These uncertainties may impair both Park’s and First Citizens’ ability to attract, retain and motivate key personnel until the merger is completed, and could cause customers and others that deal with Park and First Citizens to seek to change existing business relationships with Park and First Citizens, respectively. In addition, subject to certain exceptions, First Citizens has agreed, and will cause each of its subsidiaries, to (i) conduct its business in the ordinary course in all material respects, (ii) use reasonable best efforts to maintain and preserve intact its business organization and relationships with employees, customers and governmental entities, and advantageous business relationships and (iii) take no action that would be reasonably likely to adversely affect or materially delay the ability to obtain any necessary approvals of any regulatory agency or other governmental entity required for the transactions contemplated by the merger agreement or the ability of First Citizens to perform its covenants and agreements under the merger agreement or to consummate the transactions contemplated by the merger agreement on a timely basis.

First Citizens has also agreed not to take certain actions that could cause it to be unable to pursue other beneficial opportunities and engage in certain business activities, subject to certain exceptions, that may arise prior to the completion of the merger. Park has agreed to a more limited set of restrictions on its business activities prior to the effective time. The restrictions on each of First Citizens and Park could prevent them from pursuing certain business opportunities that arise or taking certain corporate actions prior to the effective time. See the section entitled “The Merger Agreement — Covenants and Agreements — Conduct of Business Prior to the Completion of the Merger” beginning on page 77 for a description of the restrictive covenants applicable to Park and First Citizens.

In the merger, First Citizens shareholders will become Park shareholders, and their rights as Park shareholders will be governed by Ohio law and the governing documents of Park. The rights associated with Park common stock are different from the rights associated with First Citizens common stock. See the section entitled “Comparison of Shareholders’ Rights” beginning on page 124 for a discussion of the different rights associated with Park common stock.

Holders of First Citizens voting common stock currently have the right to vote in the election of the First Citizens board of directors and on other matters affecting First Citizens. When the merger is completed, First Citizens shareholders will become Park shareholders, with a percentage ownership of Park that is smaller than their percentage ownership of First Citizens. Based on the number of shares of Park common stock and First Citizens common stock outstanding as of the close of business on the record date, and based on the number of shares of Park common stock expected to be issued in the merger, the former First Citizens shareholders, as a group, are estimated to own approximately 11% of the fully diluted

shares of Park immediately after the merger and current Park shareholders, as a group, are estimated to own approximately 89% of the fully diluted shares of Park immediately after the merger. Because of this, holders of First Citizens voting common stock will have less influence on the management and policies of the surviving corporation than they now have on the management and policies of First Citizens.

Appraisal rights (also known as dissenters’ rights) are statutory rights that, if applicable under law, enable shareholders to dissent from an extraordinary transaction, such as a merger, and to demand that the corporation pay the fair value for their shares as determined by a court in a judicial proceeding instead of receiving the consideration offered to shareholders in connection with the extraordinary transaction. If the merger agreement is adopted by First Citizens’ shareholders, First Citizens’ shareholders who do not vote in favor of First Citizens merger proposal and who properly demand payment of the fair value of their shares of First Citizens common stock under the applicable provisions of the TBCA will be entitled to appraisal rights in connection with the merger.

In addition, Park’s obligation to consummate the merger is subject to the condition that holders of no more than 7.5% of the issued and outstanding shares of First Citizens common stock demand or be entitled to receive payment of the fair value of their shares as dissenting shareholders under the applicable provisions of the TBCA. Neither First Citizens nor Park can predict the number of First Citizens shareholders who will seek payment of fair cash value of their shares. See the section entitled “The Merger — Appraisal or Dissenters’ Rights in the Merger” beginning on page 68 for more information on dissenters’ rights.

Subject to certain exceptions, the merger agreement contains “no shop” covenants that restrict First Citizens’ ability to, directly or indirectly, initiate, solicit, knowingly encourage or knowingly facilitate any inquiries or proposals with respect to, engage or participate in any negotiations with any person concerning, provide any confidential or nonpublic information or data to, or have or participate in any discussions with, any person relating to, (i) any acquisition or purchase, direct or indirect, of 25% or more of the consolidated assets of First Citizens and its subsidiaries or 25% or more of any class of equity or voting securities of First Citizens or its subsidiaries whose assets, individually or in the aggregate, constitute more than 25% of the consolidated assets of First Citizens, (ii) any tender offer or exchange offer that, if consummated, would result in such third party beneficially owning 25% or more of any class of equity or voting securities of First Citizens or its subsidiaries whose assets, individually or in the aggregate, constitute more than 25% of the consolidated assets of First Citizens or (iii) a merger, consolidation, share exchange, business combination, reorganization, recapitalization, liquidation, dissolution or similar transaction involving First Citizens or its subsidiaries whose assets, individually or in the aggregate, constitute more than 25% of the consolidated assets of First Citizens. Additionally, during the term of the merger agreement, First Citizens cannot, and cannot cause its subsidiaries and its and their representatives to on its behalf, directly or indirectly, approve or enter into any term sheet, letter of intent, indication of interest, commitment, memorandum of understanding, agreement in principle, acquisition agreement, merger agreement or other agreement relating to any acquisition proposal (whether written or oral, binding or nonbinding). See the section entitled “The Merger Agreement — Agreement Not to Solicit Other Offers” beginning on page 84 for a discussion of the no shop provisions to which First Citizens is subject under the merger agreement.

The merger agreement further provides that, during the 12-month period following the termination of the merger agreement under specified circumstances, including the entry into a definitive agreement or consummation of a transaction with respect to an acquisition proposal, First Citizens may be required to pay to Park a cash termination fee equal to $12.5 million. See the section entitled “The Merger Agreement — Termination Fee” beginning on page 87 for a more fulsome description of the circumstances that trigger First Citizens’ payment of the termination fee under the merger agreement.

These provisions could discourage a potential third-party acquirer that might have an interest in acquiring all or a significant portion of First Citizens from considering or proposing that acquisition.

You should read and consider risk factors specific to Park’s business that will also affect Park after the merger. These risks are described in the sections entitled “Risk Factors” in Park’s Annual Report on Form 10-K most recently filed with the SEC and in other documents incorporated by reference into this proxy statement/prospectus. Please see the section entitled “Where You Can Find More Information” beginning on page 137 of this proxy statement/prospectus for the location of information incorporated by reference into this proxy statement/prospectus.

This proxy statement/prospectus contains statements regarding the merger between Park and First Citizens; future financial and operating results; benefits and synergies of the transaction; future opportunities for the surviving corporation; the issuance of Park common stock contemplated by the merger agreement; the expected timing of the closing of the merger; the ability of the parties to complete the merger considering the various closing conditions and any other statements about future expectations that constitute forward-looking statements within the meaning of the federal securities laws, including the meaning of the Private Securities Litigation Reform Act of 1995, as amended, Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). From time to time, oral or written forward-looking statements may also be included in other information released to the public. Such forward-looking statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. Forward-looking statements include all statements other than statements of historical or current facts, including forecasts or trends, and are based on current expectations, assumptions, estimates and projections about Park and First Citizens or related to the merger and are subject to significant risks and uncertainties that could cause actual results to differ materially from the results expressed in such statements.

These forward-looking statements may include information about the surviving corporation’s possible or assumed future economic performance or future results of operations, including future revenues, income, expenses, provision for credit losses, provision for taxes, effective tax rate, earnings per share and cash flows and the surviving corporation’s future capital expenditures and dividends, future financial condition and changes therein, including changes in the surviving corporation’s loan portfolio and allowance for credit losses, changes in deposits, borrowings and the investment securities portfolio, future capital structure or changes therein, as well as the plans and objectives of management for the surviving corporation’s future operations, future or proposed acquisitions, the future or expected effect of acquisitions on the surviving corporation’s operations, results of operations, financial condition, and future economic performance, statements about the anticipated benefits of the proposed transaction, and statements about the assumptions underlying any such statement.

While there is no assurance that any list of risks and uncertainties or risk factors is complete, below are certain factors, in addition to the factors relating to the merger discussed under the caption entitled “Risk Factors” beginning on page 16 and the factors previously disclosed in Park’s reports filed with the SEC and incorporated by reference into this proxy statement/prospectus, which could cause actual results to differ materially from those contained or implied in the forward-looking statements or historical performance:

Additional factors that could cause results to differ materially from those described above can be found in Park’s filings with the SEC that are incorporated by reference into this proxy statement/prospectus, as described in the section entitled “Where You Can Find More Information” beginning on page 137.

All forward-looking statements are expressly qualified in their entirety by the cautionary statements set forth above. You are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this proxy statement/prospectus or the dates of the documents incorporated by reference in this proxy statement/prospectus and are based on information available at that time. Neither Park nor First Citizens assume any obligation to update forward-looking statements to reflect actual results, new information or future events, changes in assumptions or changes in circumstances or other factors affecting forward-looking statements that occur after the date the forward-looking statements were made or to reflect the occurrence of unanticipated events except as required by federal securities laws. If Park or First Citizens updates one or more forward-looking statements, no inference should be drawn that Park or First Citizens will make additional updates with respect to those or other forward-looking statements. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance on such statements.

For additional information about factors that could cause actual results to differ materially from those described in the forward-looking statements, please see the reports that Park has filed with the SEC as described under “Where You Can Find More Information” beginning on page 137.

Park and First Citizens expressly qualify in their entirety all forward-looking statements attributable to either of them or any person acting on their behalf by the cautionary statements contained or referred to in this proxy statement/prospectus.

On October 27, 2025, Park entered into a merger agreement with First Citizens. The merger agreement (a) provides that First Citizens will merge with and into Park, with Park as the surviving corporation and (b) contemplates that immediately following the completion of the merger, First Citizens National Bank will merge with and into Park National Bank, with Park National Bank as the surviving bank. Under the terms and subject to the conditions set forth in the merger agreement, each share of First Citizens common stock issued and outstanding immediately prior to the effective time of the merger (excluding dissenting shares, treasury shares and shares held by First Citizens or Park (other than the exception shares)) will be converted into the right to receive 0.52 of a share of Park common stock.

In accordance with Article 11 of Regulation S-X, the following tables show selected unaudited pro forma condensed combined financial information about the financial condition and results of operations of Park, including per share data, after giving effect to the merger and other pro forma adjustments. The unaudited pro forma condensed combined financial information assumes that the merger is accounted for under the acquisition method of accounting for business combinations in accordance with GAAP, with Park as the accounting acquirer pursuant to Accounting Standards Codification Topic 805 (“ASC 805”). The unaudited pro forma condensed combined financial information also assumes that the assets and liabilities of First Citizens will be recorded by Park at their respective fair values as of the date the merger is completed. The unaudited pro forma condensed combined statement of financial condition gives effect to the transaction as if the transaction had occurred on September 30, 2025. The unaudited pro forma condensed combined statements of operations for the nine months ended September 30, 2025, and the year ended December 31, 2024, give effect to the merger as if the merger had been completed on January 1, 2024.

The unaudited pro forma condensed combined financial data was derived from, and should be read in conjunction with, the following historical financial statements and the accompanying notes, which are included or incorporated by reference into this proxy statement/prospectus:

The unaudited pro forma condensed combined financial data should also be read together with other financial data included elsewhere or incorporated by reference into this proxy statement/prospectus.

The unaudited pro forma condensed combined financial information is presented for illustrative purposes only and does not indicate the financial position or results of operations of the combined company that would have been realized had the merger been completed at the beginning of each period presented. The pro forma adjustments are preliminary and are subject to change as additional information becomes available and as additional analysis is performed. The unaudited pro forma condensed combined financial information also does not consider any expense efficiencies, increased revenue or other potential financial benefits of the merger, nor does it consider the factors discussed in the sections entitled “Risk Factors” beginning on page 16 and “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 21. In addition, as explained in more detail in the accompanying notes, the preliminary allocation of the pro forma purchase price reflected in the unaudited pro forma condensed combined financial information is subject to adjustment and may vary significantly from the actual purchase price allocation that will be recorded upon completion of the merger. The fair values are estimates as of the date of this proxy statement/prospectus and actual amounts are still in the process of being finalized. Fair values are subject to refinement for up to one year after the closing date as additional information regarding the closing date fair values becomes available.

The unaudited pro forma condensed combined financial information of Park’s financial condition and results of operations, including per share data, are presented after giving effect to the merger. The unaudited pro forma condensed combined balance sheet as of September 30, 2025 gives effect to the merger as if the transaction had occurred on September 30, 2025. The unaudited pro forma condensed combined income statements for the nine months ended September 30, 2025 and year ended December 31, 2024, give effect to the merger as if the transaction had become effective beginning on January 1, 2024.

The merger will be accounted for using the acquisition method of accounting; accordingly, the difference between the purchase price over the estimated fair value of the assets acquired (including identifiable intangible assets) and liabilities assumed will be recorded as goodwill.

The pro forma financial information includes estimated adjustments to record the assets and liabilities of First Citizens at their respective fair values and represents management’s estimates based on available information. The pro forma adjustments included herein may be revised as additional information becomes available and as additional analysis is performed. The final allocation of the purchase price will be determined after the merger is completed and after completion of a final analysis to determine the fair values of First Citizens’ tangible, and identifiable intangible assets and liabilities as of the closing date.

All adjustments are transaction accounting adjustments as defined in Article 11-02(a)(6); no autonomous or management’s adjustments are included.

In November 2025, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2025-08, Financial Instruments—Credit Losses (Topic 326). ASU 2025-08 expands the use of the gross-up method to certain acquired loans beyond purchased financial assets with credit deterioration (“PCD”). Under ASU 2025-08, the gross-up method also applies to acquired non-PCD loans that qualify as purchased seasoned loans, which would eliminate the recognition of Day-1 credit loss expense and instead increase the amortized cost basis of such loans, affecting the pattern of interest income recognized in subsequent periods.

ASU 2025-08 is effective for interim and annual periods in fiscal years beginning after December 15, 2026, and is applied prospectively. Early adoption is permitted.

Because Park has not adopted ASU 2025-08 in its historical financial statements, the effects of this standard are not reflected in the unaudited pro forma condensed combined financial information included herein. However, had Park early adopted ASU 2025-08, the merger accounting would have resulted in the elimination of approximately $17 million of Day-1 credit loss expense, with a corresponding increase to the amortized cost basis of the acquired loan portfolio affecting the pattern of interest income recognized in subsequent periods. These potential impacts are provided for informational purposes only and do not affect the pro forma adjustments.

On October 27, 2025, Park entered into the merger agreement with First Citizens. Under the terms of the merger agreement, Park will exchange 0.52 shares of its common stock for each share of First Citizens common stock. The receipt by First Citizens shareholders of shares of Park common stock in exchange for their shares of First Citizens common stock is anticipated to qualify as a tax-free exchange. The transaction, approved or adopted by the directors of both companies, is valued at approximately $326 million. This value is based on Park’s closing stock price on December 11, 2025 of $163.81. Considering the range of Park stock prices since the announcement of the merger, the value of the transaction at closing may or may not be materially different from the transaction value included in these unaudited pro forma condensed combined financial statements.

Funding for the merger is included in the pro forma adjustments as follows (dollars in thousands):

The purchase price will depend on the market price of Park’s common shares when the acquisition is consummated. Park believes that a 10% fluctuation in the market price of its common stock is reasonably possible based on historic volatility, and the potential effect on purchase price would be:

The pro forma adjustments include the purchase accounting entries to record the merger. The excess of the purchase price over the fair value of the net assets acquired, net of deferred taxes, is allocated to goodwill. Estimated fair value adjustments included in the pro forma financial statements are based upon available information, and certain assumptions considered reasonable, and may be revised as additional information becomes available. For purposes of this pro forma analysis, fair value adjustments, other than goodwill and loans, are amortized/accreted on either a straight-line basis or under the sum-of-the-years’ digits method over their estimated average remaining lives. Fair value adjustments on loans are amortized/accreted using the effective interest method over the life of the loans. Tax expense related to the net fair value adjustments is calculated at the statutory 21% tax rate for federal income tax purposes.

Included in the pro forma adjustments are estimated core deposit intangibles of $31.0 million. The core deposit intangibles are separate from goodwill and amortized under the sum-of-the-years’ digits method over an estimated average remaining life of 10 years. When the actual amount of core deposit intangibles is determined as of the date of acquisition, which may be more or less than the estimated amount, the sum-of-the-years’ digits method will be used to record amortization over the intangibles’ actual lives. Estimated goodwill totaling $113.7 million is included in the pro forma adjustments, and is not subject to amortization, but will be tested for impairment at least annually, or when impairment indicators are identified.

The purchase price allocation reflected is preliminary. Items for which the accounting is incomplete include valuations of loans, core deposit intangibles, fixed assets, interest bearing deposits, and borrowings. The final allocation may differ materially from the amounts presented.

The allocation of the purchase price is as follows (in thousands):