Founded in 1825, Mercer County is one of 102 counties in the state of Illinois. Historically, Mercer County was formed from Schuyler County. The city of Aledo is the county seat. With FIPS code of 131, Mercer County has a population of 15,582 and area of 561 square miles (1,453 km2).
List of all cities in Mercer County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Aledo, IL | 61231 | 309 |
| Alexis, IL | 61412 | 309 |
| Boden, IL | 61281 | 309 |
| Cable, IL | 61281 | 309 |
| Eliza, IL | 61272 | 309 |
| Hamlet, IL | 61231 | 309 |
| Joy, IL | 61260 | 309 |
| Keithsburg, IL | 61442 | 309 |
| Matherville, IL | 61263 | 309 |
| Mercer, IL | 61231 | 309 |
| New Boston, IL | 61272 | 309 |
| New Windsor, IL | 61465 | 309 |
| North Henderson, IL | 61466 | 309 |
| Ohio Grove, IL | 61231 | 309 |
| Old Gilchrist, IL | 61231 | 309 |
| Preemption, IL | 61276 | 309 |
| Richland Grove, IL | 61281 | 309 |
| Seaton, IL | 61476 | 309 |
| Shale City, IL | 61231 | 309 |
| Shanghai City, IL | 61412 | 309 |
| Sherrard, IL | 61281 | 309 |
| Sunbeam, IL | 61231 | 309 |
| Viola, IL | 61486 | 309 |
| Wanlock, IL | 61231 | 309 |