644  sq mi (1,668  km² ) 601 sq mi (1,557 km²) 43 sq mi (111 km²), 6.62% Population  - ( 2000 )  - Density 140,814 233/sq mi (90/km²) Website: www.claycountygov.com Clay County is a county located in the U.S. state of Florida . As of 2000, the population was 140,814. The U.S. Census Bureau 2008 estimate for the county is