Founded in 1862, Clay County is one of 66 counties in the state of South Dakota. Historically, Clay County was formed from unorganized territory. The city of Vermillion is the county seat. With FIPS code of 27, Clay County has a population of 15,150 and area of 412 square miles (1,067 km2).
List of all cities in Clay County, SD alphabetically
| City/Town | Postal Code | Area Code |
| Burbank, SD | 57010 | 605 |
| Greenfield, SD | 57069 | 605 |
| Hub City, SD | 57069 | 605 |
| Irene, SD | 57037 | 605 |
| Mayfield, SD | 57037 | 605 |
| Meckling, SD | 57069 | 605 |
| Vermillion, SD | 57069 | 605 |
| Wakonda, SD | 57073 | 605 |
| Westerville, SD | 57069 | 605 |