EXHIBIT 21 ALLIANT ENERGY CORPORATION SUBSIDIARIES OF THE REGISTRANT The following are deemed to be significant subsidiaries of Alliant Energy Corporation as of December 31, 2001: Name of Subsidiary State of Incorporation - ------------------ ---------------------- IES Utilities Inc. Iowa Wisconsin Power and Light Company Wisconsin Interstate Power Company Delaware Alliant Energy Resources, Inc. Wisconsin Alliant Energy Investments, Inc. Iowa Alliant Energy International, Inc. Iowa Whiting Petroleum Corporation Delaware