Formed January 8, 1873 (36th county)
Sully County (1,448), Onida (664)
The Classical Revival courthouse was built in 1911. It is situated on Ash Avenue at Main Street. United States Highway 83 is eight blocks west of the site. W. M. Rich was the designer of the masonry and stone courthouse. The structure features a tower with a working clock and veterans’ memorials are on the grounds. The county was formed on January 8, 1873 as the 36th county. Cliffton was the county seat until 1884 when Onida assumed the role. It is named for Civil War General Alfred Sully. Onida is named for Oneida, New York.
Sully County government consists of a sheriff and 5 Commissioners. Three Circuit Court Judges and One Magistrate Court Judge serve Sully, Bennett, Gregory, Haakon, Hughes, Hyde, Jackson, Jones, Lyman, Mellette, Potter, Stanley, Todd, and Tripp counties. The county is located in the center of the state. Pierre, South Dakota is directly south and Rapid City, South Dakota is southwest of the county. The Missouri River forms its western border. The county center is 5.4 miles North of Onida nearer Agar. The county is surrounded clockwise by Potter, Hyde, Hughes, Stanley, and Dewey counties.
The area of the county is 1007 square miles. It is 30 out of 66 in the state. It ranks 62 out of 66 in population in the state. It has a density of 1.4 persons per square mile making it 61 out of 66 in the state. Sully County has 50.5% of its population in its incorporated areas. United States Highway 83 travels through the county from north to south from Potter County to Hughes County. The county looks like a baby’s bottle lying on its side. Onida is located east of center in the county. Onida is the county seat and the largest city. It is 45.9% of the county population. The county seat is pronounced OE-NIE-DA.
Agar
Onida
