Brown County, South Dakota

Brown County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 38,301, making it the fourth most populous county in South Dakota, and was estimated to be 37,561 in 2025. Its county seat is Aberdeen. The county is named for Alfred Brown, of Hutchinson County, South Dakota, a Dakota Territorylegislator in 1879.

Brown County is part of the Aberdeen, SD Micropolitan Statistical Area.