Middlesex -- U.S. County in New Jersey Population (2000): 750162 Housing Units (2000): 273637 Land area (2000): 309.719506 sq. miles (802.169805 sq. km) Water area (2000): 12.792287 sq. miles (33.131870 sq. km) Total area (2000): 322.511793 sq. miles (835.301675 sq. km) Located within: New Jersey (NJ), FIPS 34 Location: 40.494044 N, 74.383918 W Headwords: Middlesex Middlesex, NJ Middlesex County Middlesex County, NJ