Post Offices List in Barnwell County, South Carolina:
| Barnwell Post Office | 221 Main St, Barnwell, SC 29812 |
| Blackville Post Office | 476 Main St, Blackville, SC 29817 |
| Elko Post Office | 10049 Us Highway 78, Elko, SC 29826 |
| Williston Post Office | 12926 Main St, Williston, SC 29853 |
| Hilda Post Office | 75 Railroad Ave, Barnwell, SC 29812 |