There are 7 US Post Offices in Brookings County serving a total of 30,264 residents equating to 4,323 residents per post office. It's estimated that approximately 48,305 packages are handled across the 7 county post offices annually. Brookings County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 31,965, making it the fifth-most populous county in South Dakota. Its county seat is Brookings. The county was created in 1862 and organized in 1871. Brookings County comprises the Brookings, SD Micropolitan Statistical Area."