Founded in 1862, Union County is one of 66 counties in the state of South Dakota. Historically, Union County was formed from unorganized territory. The city of Elk Point is the county seat. With FIPS code of 127, Union County has a population of 16,872 and area of 460 square miles (1,191 km2).
List of all cities in Union County, SD alphabetically
| City/Town | Postal Code | Area Code |
| Alcester, SD | 57001 | 605 |
| Alsen, SD | 57004 | 605 |
| Beresford, SD | 57004 | 605 |
| Big Springs, SD | 57001 | 605 |
| Dakota Dunes, SD | 57049 | 605 |
| Elk Point, SD | 57025 | 605 |
| Emmet, SD | 57004 | 605 |
| Jefferson, SD | 57038 | 605 |
| Junction City, SD | 57025 | 605 |
| McCook Lake, SD | 57049 | 605 |
| Nora, SD | 57001 | 605 |
| North Sioux City, SD | 57049 | 605 |
| Richland, SD | 57025 | 605 |
| Spink, SD | 57025 | 605 |