Belle Fourche is a city in and the county seat of Butte County, South Dakota, United States. The population was 5,594 at the 2010 census. Belle Fourche is the site of the geographic center of the fifty United States. (Lebanon, Kansas claims the title for the 48 contiguous states.) According to the United States Census Bureau, the city has a total area of 8.6 square miles (22.29 km²), of which, 8.53 square miles (22.1 km²) of it is land and 0.07 square miles (0.19 km²) is water.