Piatt -- U.S. County in Illinois Population (2000): 16365 Housing Units (2000): 6798 Land area (2000): 440.021826 sq. miles (1139.651250 sq. km) Water area (2000): 0.312242 sq. miles (0.808703 sq. km) Total area (2000): 440.334068 sq. miles (1140.459953 sq. km) Located within: Illinois (IL), FIPS 17 Location: 39.997207 N, 88.577414 W Headwords: Piatt Piatt, IL Piatt County Piatt County, IL