There are 10 US Post Offices in Brown County serving a total of 35,903 residents equating to 3,590 residents per post office. It's estimated that approximately 57,305 packages are handled across the 10 county post offices annually. Brown County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 36,531, making it the fourth-most populous county in South Dakota. Its county seat is Aberdeen. The county is named after Alfred Brown, of Hutchinson County, South Dakota, a Dakota Territory legislator in 1879. Brown County is part of the Aberdeen, SD Micropolitan Statistical Area."