Founded in 1845, Mercer County is one of 114 counties in the state of Missouri. Historically, Mercer County was formed from Grundy County. The city of Princeton is the county seat. With FIPS code of 129, Mercer County has a population of 3,488 and area of 454 square miles (1,176 km2).
List of all cities in Mercer County, MO alphabetically
| City/Town | Postal Code | Area Code |
| Mercer, MO | 64661 | 660 |
| Princeton, MO | 64673 | 660 |