Exhibit 21
Affiliates and Subsidiaries of Integrys Energy Group, Inc. December 31, 2007
INTEGRYS ENERGY GROUP, INC.+ *
	Wisconsin Public Service Corporation+
		WPS Leasing, Inc.+
		Wisconsin Valley Improvement Company (27.1% ownership) +
		Wisconsin River Power Company (50% ownership)+
		WPS Investments, LLC (approximately 17.3% ownership)+
			American Transmission Company LLC (approximately 34.54% ownership)+
		ATC Management Inc. (32.58% ownership)+
	WPS Investments, LLC (approximately 77.93% ownership)+
		American Transmission Company LLC (approximately 34.54% ownership)+
	WPS Nuclear Corporation+
	Michigan Gas Utilities Corporation++
	Minnesota Energy Resources Corporation++
	Integrys Business Support, LLC++
	WPS Visions, Inc.+
	Badger Energy Services, LLC (12.50% ownership)+
	Integrys Energy Services, Inc.+
		Quest Energy, LLC+++
		Integrys Energy Services of Canada Corp. (formed under Canadian law)
		Integrys Energy Services of New York, Inc. (formed under New York law)
		Integrys Energy Services of Texas, LP (formed under Texas law)
		PERC Holdings, LLC++
		WPS Power Development, LLC+
			PDI Stoneman, Inc.+
					Mid-American Power, LLC+
			Winnebago Energy Center, LLC++
			WPS Canada Generation, Inc.+
			WPS New England Generation, Inc.+
			Wisconsin Woodgas LLC+
			Wisconsin Energy Operations LLC (49% ownership)+
			ECO Coal Pelletization #12 LLC (70% ownership)++
				Synfuel Solutions, LLC (33.33% ownership)++
						Synfuel Solutions Operating, LLC++
			Sunbury Holdings, LLC++
				WPS Westwood Generation, LLC++
			WPS Empire State, Inc. (formed under New York law)
				WPS Beaver Falls Generation, LLC++
				WPS Syracuse Generation, LLC++
			Combined Locks Energy Center, LLC+
			PV Midstream Ventures, LLC (50% ownership)++
			Peoples Natural Gas Liquids, LLC++

Affiliates and Subsidiaries of Integrys Energy Group, Inc. December 31, 2007
INTEGRYS ENERGY GROUP, INC.+*
	Peoples Energy Corporation++++
		The Peoples Gas Light and Coke Company++++
			Peoples Gas Neighborhood Development Corporation++++
		North Shore Gas Company++++
		Peoples Energy Services Corporation++++
		Peoples Energy Resources Company, LLC++
			Peoples MW, LLC++
			PERC Power, LLC++
					Peoples Elwood, LLC++
						Elwood Energy, LLC (50% ownership)++
		Peoples District Energy Corporation++++
		Peoples Energy Ventures, LLC++
			Peoples Energy Home Services, LLC++
			Peoples Energy Neighborhood Development, LLC++
			Peoples Technology, LLC++
	Upper Peninsula Power Company+++
		WPS Investments, LLC (approximately 4.76% ownership)+
				American Transmission Company LLC (approximately 34.54% ownership)+
		ATC Management Inc. (1.96% ownership)+
	Upper Peninsula Building Development Company+++
	Penvest, Inc.+++
*	Integrys Energy Group, Inc. is the parent holding company.  All affiliated companies listed are 100% owned except asnoted otherwise.  All affiliates are currently active, with the exception of Wisconsin Woodgas, LLC,  Synfuel Solutions, LLC, and (checking on PEC companies).
+	Formed under Wisconsin law
++	Formed under Delaware law
+++	Formed under Michigan law
++++	Formed under Illinois law