Belle Fourche is a city in and the county seat of Butte County, South Dakota, United States. The population was 5,617 at the 2020 census, and was estimated to be 5,855 in 2024, making it the 18th-most populous city in South Dakota. It is near the geographic center of the United States, which moved some 550 miles northwest from the geographic center of the contiguous United States in Lebanon, Kansas with the admission of Alaska and Hawaii in the mid-20th century.