|                                                                                 |                                                                           | Exhibit 21                                           |
|--------------------------------------------------------------------------------------|--------------------------------------------------------------------------------|-----------------------------------------------------------|
| Affiliates and Subsidiaries of Wisconsin Public Service CorporationDecember 31, 2010 |
|                                                                                 |
|                                                                                 | Wisconsin Public Service Corporation+                                          |
|                                                                                 |                                                                           | WPS Leasing, Inc.+                                        |
|                                                                                 |                                                                           | Wisconsin Valley Improvement Company (27.1% ownership)+   |
|                                                                                 |                                                                           | Wisconsin River Power Company (50% ownership)+            |
|                                                                                 |                                                                           | WPS Investments, LLC (approximately 12.54% ownership)+    |
|                                                                                 |                                                                           |                                                      | American Transmission Company LLC (approximately 34.07% ownership)+ |
|                                                                                 |                                                                           | ATC Management Inc. (32.11% ownership of Class A shares)+ |
|                                                                                 |                                                                           |
|                                                                                 | All affiliated companies listed are 100% owned except as noted otherwise. |
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| +                                                                                    | Formed under Wisconsin law                                                     |
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