| Company | State of Organization | ||||
| BTD Manufacturing, Inc. | Minnesota | ||||
| Northern Pipe Products, Inc. | North Dakota | ||||
| Otter Tail Assurance Limited | Cayman Islands | ||||
| Otter Tail Power Company | Minnesota | ||||
| T.O. Plastics, Inc. | Minnesota | ||||
| Varistar Corporation | Minnesota | ||||
| Vinyltech Corporation | Arizona | ||||