Illiopolis is a village in Sangamon County, Illinois, United States. The population was 916 at the 2000 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 / 39.85139; -89.24722 (39.851351, -89.247131).
According to the United States Census Bureau, the village has a total area of 0.4 square miles (1.2 km²), all of it land.