Mercer -- U.S. County in Pennsylvania Population (2000): 120293 Housing Units (2000): 49859 Land area (2000): 671.815970 sq. miles (1739.995300 sq. km) Water area (2000): 10.757464 sq. miles (27.861703 sq. km) Total area (2000): 682.573434 sq. miles (1767.857003 sq. km) Located within: Pennsylvania (PA), FIPS 42 Location: 41.294427 N, 80.313128 W Headwords: Mercer Mercer, PA Mercer County Mercer County, PA