Monroe -- U.S. County in Illinois Population (2000): 27619 Housing Units (2000): 10749 Land area (2000): 388.291968 sq. miles (1005.671538 sq. km) Water area (2000): 9.417843 sq. miles (24.392101 sq. km) Total area (2000): 397.709811 sq. miles (1030.063639 sq. km) Located within: Illinois (IL), FIPS 17 Location: 38.329154 N, 90.175233 W Headwords: Monroe Monroe, IL Monroe County Monroe County, IL