Mercer County is a county in Missouri, United States, tucked against the Iowa border in the state’s northwestern corner. It had a population of 3,538 at the 2020 census, one of the smallest county totals in Missouri, and covers 455 square miles (1,180 km2) centred near 40°25′N 93°34′W.
Princeton is the county seat, and its postal code is 64673. The county has two incorporated cities, one village, one census-designated place, and a scatter of unincorporated communities and rural crossroads. Mercer County sits in the Central time zone.
Towns & Villages in Mercer County
Mercer County has two incorporated cities — Princeton (the county seat) and Mercer — plus the village of South Lineville and the census-designated place of Ravanna. The rest of the list below is unincorporated communities and former post-office settlements, several no larger than a farm crossroads today.
| Place | Type | Pop. | ZIP |
|---|---|---|---|
| Princeton | City · seat | — | 64673 |
| Mercer | City | — | 64661 |
| South Lineville | Village | — | — |
| Ravanna | CDP | — | — |
| Adel | Unincorp. | — | — |
| Burrows | Unincorp. | — | — |
| Cleopatra | Unincorp. | — | — |
| Dinsmore | Unincorp. | — | — |
| Goshen | Unincorp. | — | — |
| Half Rock | Unincorp. | — | — |
| Mill Grove | Unincorp. | — | — |
| Modena | Unincorp. | — | — |
| Saline | Unincorp. | — | — |
| Topsy | Unincorp. | — | — |
| Wataga | Unincorp. | — | — |
South Lineville sits directly on the Iowa state line, and several of the unincorporated names above — including Goshen and Half Rock — mark former post offices or rail sidings rather than active settlements today.
ZIP Codes
- 64673 — Princeton (also serves South Lineville, Ravanna, and most of the rural county)
- 64661 — Mercer
Mercer County has just two ZIP codes; unincorporated communities without a post office of their own use whichever of Princeton or Mercer is closer.
Geography
Mercer County is rolling, mostly cleared farmland drained by the Weldon River and Big Creek, both part of the Grand River watershed. Of its 455 square miles, 454 are land and about 1.3 square miles are water.
It borders Wayne County, Iowa to the north, Decatur County, Iowa to the northwest, Putnam County to the east, Sullivan County to the southeast, Grundy County to the south, and Harrison County to the west.
Demographics
Mercer County’s 2020 census population was 3,538, giving a density of roughly 7.8 people per square mile of land — among the lowest of any Missouri county. Princeton and Mercer are its two largest communities. Rural, sparsely populated counties like this one typically run well below the Missouri median household income of $68,545, and Mercer County is no exception.
Economy & Local Life
Agriculture drives the local economy — row crops of corn and soybeans on the flatter ground, cattle grazing on the rolling pasture that covers much of the county. Princeton, as the seat, hosts the county courthouse and the Mercer County R-II school district, the largest employers outside farming itself. Livestock auctions and grain elevators around Princeton and Mercer remain the main commercial activity beyond the farms themselves, typical of the sparsely populated counties along Missouri’s northern border.
History
Mercer County was organized on February 14, 1845, carved out of neighboring Grundy County, and named for General Hugh Mercer, a Revolutionary War officer killed at the Battle of Princeton — the same battle that gave the county seat its name. During the Civil War the county leaned strongly Unionist: fewer than 20 Mercer County men are recorded fighting for the Confederacy, against well over 1,000 who volunteered for Union service.
Getting There
US Route 136 crosses the county east–west through Princeton, and Missouri Route 5 runs north–south through the same town, the county’s main road junction.
- Bethany, Missouri — about 24 miles west via US-136
- Unionville, Missouri — about 24 miles east via US-136
- Trenton, Missouri — about 26 miles south via MO-5
- Chillicothe, Missouri — about 45 miles south
The nearest commercial air service is Kirksville Regional Airport, roughly 60 miles east; the nearest major hub is Kansas City International Airport, roughly 130 miles southwest.
Frequently Asked Questions
Where is Mercer County, Missouri?
It is in the state’s northwestern corner, on the Iowa border, centred near 40°25′N 93°34′W.
What is the population of Mercer County?
It had a population of 3,538 at the 2020 census.
How big is Mercer County?
It covers 455 square miles (1,180 km2), of which 454 square miles is land.
What is the county seat of Mercer County?
Princeton is the county seat.
How many towns are in Mercer County?
The county has two incorporated cities (Princeton and Mercer), one village (South Lineville), one census-designated place (Ravanna), and a number of small unincorporated communities.
What ZIP codes are in Mercer County?
64673 (Princeton) and 64661 (Mercer) cover the whole county.
Who is Mercer County named after?
General Hugh Mercer, a Revolutionary War officer killed at the Battle of Princeton, New Jersey — the county seat takes its name from the same battle.
More counties in this state: Towns and villages in Missouri.