| Locality | Post Code |
|---|---|
| Aledo, Mercer | 61231 |
| Boden, Mercer | 61281 |
| Cable, Mercer | 61281 |
| Hamlet, Mercer | 61231 |
| Joy, Mercer | 61260 |
| Keithsburg, Mercer | 61442 |
| Matherville, Mercer | 61263 |
| Mercer, Mercer | 61231 |
| New Boston, Mercer | 61272 |
| New Windsor, Mercer | 61465 |
| North Henderson, Mercer | 61466 |
| Ohio Grove, Mercer | 61231 |
| Old Gilchrist, Mercer | 61231 |
| Preemption, Mercer | 61276 |
| Richland Grove, Mercer | 61281 |
| Seaton, Mercer | 61476 |
| Shale City, Mercer | 61231 |
| Shanghai, Mercer | 61412 |
| Sherrard, Mercer | 61281 |
| Sunbeam, Mercer | 61231 |
| Viola, Mercer | 61486 |
| Wanlock, Mercer | 61231 |