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).

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 2015, the company finalized the sale of its Minnesota territory to a consortium of 12 electric cooperatives operating in that state.

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