Ameren Illinois Company operates in rate-regulated electric and natural gas transmission and distribution businesses in Illinois. It supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. The company was formerly known as Central Illinois Public Service Company and changed its name to Ameren Illinois Company in October 2010. Ameren Illinois Company was founded in 1902 and is based in Collinsville, Illinois. Ameren Illinois Company is a subsidiary of Ameren Corporation.