Sponsored Topics. Hartsville is a small city in Darlington County, South Carolina, United States. The population was 7,764 at the 2010 census. Hartsville is located at 34Â°22â²10â³N 80Â°4â²51â³W / 34.36944Â°N 80.08083Â°W / 34.36944; -80.08083 (34.369474, -80.080783). According to the United States Census Bureau, the city has a total area of 5.0 square miles (13.0 kmÂ²).