Interstate Power and Light Company (IPL) expanded greatly in the late 1920s to include operations in Iowa, Wisconsin, Minnesota, North and South Dakota, Nebraska, Oklahoma, and Manitoba (Canada).

During the 1940s, IPC divested itself of all its operations that were not part of its main territory in southern MN / northern Iowa.

The largest chunk of territory was that operating in northeast ND / northern MN / Emerson, Manitoba which was sold in summer 1943 and fall 1944.

[3] Today, IPL provides electricity and gas to communities in Iowa, while WPL serves southern and central Wisconsin.

In the 1970s IES constructed the Duane Arnold Energy Center, a 615 MW nuclear plant in Palo, Iowa.

In 2016, Alliant began offering a $500 rebate for its customers who purchase a home charging station for electric vehicles.