Montgomery -- U.S. County in Illinois Population (2000): 30652 Housing Units (2000): 12525 Land area (2000): 703.795231 sq. miles (1822.821203 sq. km) Water area (2000): 5.955614 sq. miles (15.424970 sq. km) Total area (2000): 709.750845 sq. miles (1838.246173 sq. km) Located within: Illinois (IL), FIPS 17 Location: 39.207454 N, 89.500917 W Headwords: Montgomery Montgomery, IL Montgomery County Montgomery County, IL