There are 6 US Post Offices in Kingsbury County serving a total of 5,918 residents equating to 986 residents per post office. It's estimated that approximately 9,446 packages are handled across the 6 county post offices annually. Kingsbury County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 5,148. Its county seat is De Smet. The county was created in 1873 and organized in 1880. It was named for brothers George W. and T. A. Kingsbury, descendants of the colonial English Kingsbury family in Boston, Massachusetts. They were prominently involved in the affairs of Dakota Territory and served as elected members of several Territorial Legislatures."