(2,722 km?) 215 sq mi (557 km?), 17.00% Population - ( 2006(est.) ) - Density 1,177,060 951/sq mi (367/km?) Website: www.hillsboroughcounty.org Hillsborough County is a county located in the U.S. state of Florida . The 2000 population was 998,948. In 2007, the Hillsborough County Planning Commission conducted a population estimate that