Greenville County is located in the U.S. state of South Carolina. As of the 2020 census, the population was 525,534, making it the most populous county in the state. Its county seat is Greenville. The county is also home to the Greenville County School District, the largest school system in South Carolina. County government is headquartered at Greenville County Square. Greenville County is the most populous county in Upstate South Carolina as well as the state.