On October 1, 2010 Ameren's three Illinois operating companies merged to become Ameren Illinois Company. The merger resulted in a single operating company providing power to most of downstate Illinois. However, the Ameren Illinois service territory is split into three rate zones corresponding to the service territories of the three former Illinois operating companies—Zone I (the former AmerenCIPS), Zone II (the former AmerenCILCO) and Zone III (the former AmerenIP). On the same date, AmerenUE changed its name to Ameren Missouri Company. The former Illinois portion of the AmerenUE territory was transferred to Ameren Illinois Zone I.