Sully County, South Dakota, organized in 1883, is located in central South Dakota, thirty miles north from South Dakota's State Capital, Pierre. The county is named after General Alfred Sully, who built Fort Sully near the Missouri River.  Sully County has two communities, Agar and Onida. Onida is the County Seat and this is where the courthouse is located.

 

Population (2000 Census): 1,556

Total Area: 1,070 Square Miles