Exhibit 21 BLACK HILLS POWER, INC. ACTIVE WHOLLY OWNED DIRECT AND INDIRECT SUBSIDIARIES Acquisition Partners, LP, a New York limited partnership Adirondack Hydro - Fourth Branch, LLC, a New York limited liability company Adirondack Hydro Development Corporation, a Delaware corporation Adirondack Operating Services, LLC, a New York limited liability company Black Hills Colorado, LLC, a Delaware limited liability company Black Hills Energy Capital, Inc., a Delaware corporation Black Hills Fountain Valley, LLC, a Delaware limited liability company Black Hills Idaho Operations, LLC, a Delaware limited liability company Black Hills Long Beach, Inc., a Delaware corporation Black Hills Nevada Operations, LLC, a Delaware limited liability company Black Hills Nevada Real Estate Holdings, LLC, a Delaware limited liability company Black Hills Nevada, LLC, a Delaware limited liability company Black Hills North America, Inc., a Delaware corporation Black Hills Southwest, LLC, a Delaware limited liability company Black Hills Valmont Colorado, Inc., a Delaware corporation E NextA Equipment Leasing Company, LLC, a Delaware limited liability company EIF Investors, Inc., a Delaware corporation Fountain Valley Power, LLC, a Delaware limited liability company Hudson Falls, LLC, a New York limited liability company 1 Las Vegas Cogeneration Energy Financing Company, LLC, a Delaware limited liability company Las Vegas Cogeneration II, LLC, a Delaware limited liability company Middle Falls Corporation, a New York Corporation Middle Falls II, LLC, a New York limited liability company NHP, LP, a New York limited partnership North American Funding, LLC, a Delaware limited liability company NYSD Limited Partnership, a New York limited partnership NYSD Partners, LLC, a New York limited liability company Sissonville Corporation, a New York corporation Sissonville II, LLC, a New York limited liability company Sissonville Limited Partners, LLC, a New York limited liability company Sissonville Limited Partnership, a New York limited partnership South Glens Falls, LLC, a Delaware limited liability company State Dam Corporation, a New York corporation State Dam II, LLC, a New York limited liability company Sunco Ltd., LLC, a Nevada limited liability company Warrensburg Corporation, a New York corporation Warrensburg Hydro Power Limited Partnership, a New York limited partnership Warrensburg II Corporation, a New York corporation 2