Carterville is a city in Williamson County, Illinois, United States. At the 2020 census, the city's population was 5,848. The city is part of the Carbondale-Marion-Herrin combined statistical area and has grown considerably as a residential community of Carbondale and Marion.

Williamson County is a county in Southern Illinois. At the 2020 census, it had a population of 67,153. The largest city and county seat is Marion.