Ameren Illinois Company, doing business as Ameren Illinois, engages in the rate-regulated electric generation, transmission, and distribution business in Illinois. It also engages in the natural gas distribution business. Ameren Illinois Company was formerly known as Central Illinois Public Service Company and changed its name to Ameren Illinois Company in October 2010. The company was founded in 1902 and is headquartered in Collinsville, Illinois. Ameren Illinois Company operates as a subsidiary of Ameren Corporation.