4 zips
| Zip Code | City | Population ↓ |
|---|---|---|
| 57049 | North Sioux City | 7,962 |
| 57025 | Elk Point | 3,120 |
| 57038 | Jefferson | 1,796 |
| 57001 | Alcester | 1,540 |
The data shown reflect ZCTAs from the US Census. As of 2024, there are 4 ZCTAs in Union County, South Dakota (US Census).