Illiopolis is a village in Sangamon County, Illinois, United States. The population was 891 at the 2010 census. It is part of the Springfield, Illinois Metropolitan Statistical Area.
Illiopolis is located at 39°51′5″N 89°14′50″W / 39.85139°N 89.24722°W (39.851351, -89.247131).
The name was formed from Illinois and -polis, a Greek suffix meaning "city".