) 27 sq mi (70 km²), 2.72% New York's location in the U.S. Population  - ( 2000 )  - Density 73,966 75/sq mi (29/km²) Website: co.sullivan.ny.us Sullivan County is a county located in the U.S. state of New York . According to the 2007 estimate by the U.S. Census Bureau , the county's population was 76,303.