Post Offices List in Union County, South Dakota:
| Alcester Post Office | 111 Dakota St, Alcester, SD 57001 |
| Beresford Post Office | 100 S 3rd St, Beresford, SD 57004 |
| Elk Point Post Office | 123 W Main St, Elk Point, SD 57025 |
| Jefferson Post Office | 303 Main St, Jefferson, SD 57038 |
| North Sioux City Post Office | 310 N Derby Ln, North Sioux City, SD 57049 |