Clay -- U.S. County in Missouri Population (2000): 184006 Housing Units (2000): 76230 Land area (2000): 396.348219 sq. miles (1026.537131 sq. km) Water area (2000): 12.515353 sq. miles (32.414613 sq. km) Total area (2000): 408.863572 sq. miles (1058.951744 sq. km) Located within: Missouri (MO), FIPS 29 Location: 39.253674 N, 94.474033 W Headwords: Clay Clay, MO Clay County Clay County, MO