Sully County, South Dakota

Sully County
Sully Courthouse (2013)
Location within the U.S. state of South Dakota
South Dakota's location within the U.S.
Coordinates: 44°43′20.37″N 100°07′53.036″W / 44.7223250°N 100.13139889°W / 44.7223250; -100.13139889
Country United States
State South Dakota
Founded1873 (created)
1883 (organized)
Named afterAlfred Sully
SeatOnida
Largest cityOnida
Area
  Total
1,070 sq mi (2,800 km2)
  Land1,007 sq mi (2,610 km2)
  Water63 sq mi (160 km2)  5.9%
Population
 (2020)
  Total
1,446
  Estimate 
(2024)
1,468
  Density1.4/sq mi (0.52/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional districtAt-large
Websitewww.sullycounty.net

Sully County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 1,446, making it the fifth-least populous county in South Dakota. Its county seat is Onida. The county was created in 1873 and organized in 1883. It is named after General Alfred Sully, who built Fort Sully.

Sully County is included in the Micropolitan Statistical Area of Pierre.

Sully County was the location of the largest African American homesteader settlement in the state, the Blair Colony. An Illinois man named Norvel Blair arrived in Fairbank Township in 1884, after sending his sons Benjamin and Patrick to investigate the area for settlement. Blair's financial success, achieved through farming and breeding racehorses, attracted dozens of other Black families to the colony. Blair became the first Black South Dakotan to serve on a school board.

The decline of South Dakota agriculture during the Great Depression led most Blair Colony residents to seek work in larger cities like Minneapolis and Chicago. A historical marker in the county seat of Onida remembers the colony.