Kingsbury County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 5,187. Its county seat is De Smet. The county was created in 1873, and was 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.