|                                                                                           |                                                                                     | Exhibit      21                                                                                 |
|------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------|
| Affiliates      and Subsidiaries of Wisconsin Public Service CorporationDecember      31, 2009 |
|                                                                                           |
|                                                                                           | Wisconsin      Public Service Corporation+                                               |
|                                                                                           |                                                                                     | WPS Leasing,      Inc.+                                                                              |
|                                                                                           |                                                                                     | Wisconsin      Valley Improvement Company (27.1% ownership)+                                         |
|                                                                                           |                                                                                     | Wisconsin      River Power Company (50% ownership)+                                                  |
|                                                                                           |                                                                                     | WPS      Investments, LLC (approximately 12.77% ownership)+                                          |
|                                                                                           |                                                                                     |                                                                                                 | American      Transmission Company LLC (approximately 34.07%  ownership)+ |
|                                                                                           |                                                                                     | ATC Management      Inc. (32.11% ownership of Class A shares, 20% ownership of Class B      shares)+ |
|                                                                                           |                                                                                     |
|                                                                                           | All affiliated      companies listed are 100% owned except as noted      otherwise. |
| +                                                                                              | Formed under      Wisconsin law                                                          |
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