Custer County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 8,318. Its county seat is Custer. The county was created in 1875, and was organized in 1877. It was named after General George Armstrong Custer.

Custer is a city in Custer County, South Dakota, United States. The population was 1,919 at the 2020 census. It is the county seat of Custer County.