Founded in 1873, Sully County is one of 66 counties in the state of South Dakota. Historically, Sully County was formed from Potter County. The city of Onida is the county seat. With FIPS code of 119, Sully County has a population of 1,476 and area of 1,007 square miles (2,608 km2).
List of all cities in Sully County, SD alphabetically
| City/Town | Postal Code | Area Code |
| Agar, SD | 57520 | 605 |
| Kasper, SD | 57564 | 605 |
| Onida, SD | 57564 | 605 |