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 two brothers, George W. and T. A. Kingsbury of the prominent Kingsbury family, who were prominently involved in the affairs of Dakota Territory (which, at that time, the county was located in) and members of several Territorial Legislatures.