| Locality | Post Code |
|---|---|
| Alcester, Union | 57001 |
| Alsen, Union | 57004 |
| Beresford, Union | 57004 |
| Big Springs, Union | 57001 |
| Dakota Dunes, Union | 57049 |
| Elk Point, Union | 57025 |
| Emmet, Union | 57004 |
| Jefferson, Union | 57038 |
| Junction City, Union | 57025 |
| McCook Lake, Union | 57049 |
| Nora, Union | 57001 |
| North Sioux City, Union | 57049 |
| Richland, Union | 57025 |
| Spink, Union | 57025 |