Deuel County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 4,295. Its county seat is Clear Lake. The county was created in 1862, and was organized in 1878. It is named for Jacob Deuel, a legislator in 1862.

Brookings County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 34,375, 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.