EXHIBIT 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of Community Financial System, Inc. of our report dated February 28, 2025 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in Community Financial System, Inc.'s Annual Report on Form 10-K for the year ended December 31, 2024. 

/s/ PricewaterhouseCoopers LLP

Buffalo, New York 

May 30, 2025