Fort Mill, also known as Fort Mill Township, is a town in York County, South Carolina, United States. It is a suburb of Charlotte, North Carolina. As of the 2020 census, the population of the town was 24,521. Some businesses and residents in the Indian Land community of neighboring Lancaster County share a Fort Mill mailing address, but the official to…Fort Mill, also known as Fort Mill Township, is a town in York County, South Carolina, United States. It is a suburb of Charlotte, North Carolina. As of the 2020 census, the population of the town was 24,521. Some businesses and residents in the Indian Land community of neighboring Lancaster County share a Fort Mill mailing address, but the official town boundary extends only within York County.