Sullivan is a city in Moultrie County, Illinois, United States. The population was 4,326 at the 2000 census, and 4,396 in 2009. It is the county seat of Moultrie County. Sullivan is named after Revolutionary War general John Sullivan.
Sullivan is located at 39°35′54″N 88°36′36″W / 39.59833°N 88.61°W / 39.59833; -88.61 (39.598270, -88.610038).
According to the United States Census Bureau, the city has a total area of 2.0 square miles (5.3 km²), all of it land.