In the late 1920s and early 1930s, CIPSCO linked its power lines to several communities served by Illinois Power and Light Corp., and contracted for power with the Missouri General Utilities Co.

With the added generating capabilities of a 55,000-kilowatt unit at the Powerton Power Station of the Super-Power Company of Illinois, in which CIPSCO had an interest, and a second 55,000-kilowatt unit under construction, CIPSCO began offering electricity to communities outside its immediate service area.

In early 1934, CIPSCO introduced natural gas to the remaining interconnected area previously supplied with artificial gas. With this step, CIPSCO made gas service available to 95 percent of its electric customers.

In the 1940s, CIPSCO began to build power plants in Illinois, and by 1979 the company had constructed five coal-fired plants generating 2,900 megawatts of electricity.