Washington County is a county in Missouri, United States, in the south-eastern Ozark foothills between St. Louis and the Bootheel. It had a population of 23,514 at the 2020 census and covers 762 square miles (1,970 km2) centred near 37°58′N 90°53′W.
Potosi is the county seat, and its postal code is 63664. The county has 2 incorporated cities, 2 villages, and 1 census-designated place, alongside dozens of unincorporated communities left over from a century and a half of lead, barite, and iron mining. Washington County is in the Central time zone.
Towns & Villages in Washington County
Washington County has only a handful of incorporated places — Potosi and Irondale hold city charters, Caledonia and Mineral Point are villages, and Terre du Lac is a census-designated place around a private lake community. Everything else on the list below is an unincorporated community: mining camps, mill sites, and crossroads hamlets that never organized as towns. Many trace their names to the county’s 19th- and 20th-century lead and barite (locally “tiff”) mining industry.
| Place | Type | Pop. | ZIP |
|---|---|---|---|
| Potosi | City · seat | — | 63664 |
| Irondale | City | — | — |
| Caledonia | Village | 131 | 63631 |
| Mineral Point | Village | — | — |
| Terre du Lac | CDP | — | — |
| Anthonies Mill | Unincorp. | — | — |
| Aptus | Unincorp. | — | — |
| Barytes | Unincorp. | — | — |
| Bates Creek Camp | Unincorp. | — | — |
| Belgrade | Unincorp. | — | — |
| Bellefontaine | Unincorp. | — | — |
| Bliss | Unincorp. | — | — |
| Brazil | Unincorp. | — | — |
| Cadet | Unincorp. | — | — |
| Camp Lakewood | Unincorp. | — | — |
| Cannon Mines | Unincorp. | — | — |
| Courtois | Unincorp. | — | — |
| Cruise Mill | Unincorp. | — | — |
| Delbridge | Unincorp. | — | — |
| Ebo | Unincorp. | — | — |
| Fertile | Unincorp. | — | — |
| Floyd | Unincorp. | — | — |
| Fountain Farm | Unincorp. | — | — |
| French Town | Unincorp. | — | — |
| Frogtown | Unincorp. | — | — |
| Happy Hollow | Unincorp. | — | — |
| Holiday Shores | Unincorp. | — | — |
| Hopewell | Unincorp. | — | — |
| Horton Town | Unincorp. | — | — |
| Hulsey | Unincorp. | — | — |
| Hurricane | Unincorp. | — | — |
| Ishmael | Unincorp. | — | — |
| Latty | Unincorp. | — | — |
| Levy | Unincorp. | — | — |
| Maddens Richwoods | Unincorp. | — | — |
| Mud Town | Unincorp. | — | — |
| Northcut | Unincorp. | — | — |
| Old Mines | Unincorp. | — | — |
| Palmer | Unincorp. | — | — |
| Pea Ridge | Unincorp. | — | — |
| Peoria | Unincorp. | — | — |
| Quaker | Unincorp. | — | — |
| Rabbitville | Unincorp. | — | — |
| Racola | Unincorp. | — | — |
| Richwoods | Unincorp. | — | — |
| Robidoux | Unincorp. | — | — |
| Shibboleth | Unincorp. | — | — |
| Shirley | Unincorp. | — | — |
| Springtown | Unincorp. | — | — |
| Summit | Unincorp. | — | — |
| Sunlight | Unincorp. | — | — |
| Theabeau Town | Unincorp. | — | — |
| Tiff | Unincorp. | — | — |
Old Mines is the county’s oldest settlement, founded by French lead miners in the early 1700s and still the heart of the “Paw-Paw French” dialect community, one of the last pockets of Missouri French speakers in the country. Tiff takes its name from the local miners’ term for barite ore.
Townships
Washington County is divided into civil townships, including Belgrade, Breton, Concord, Harmony, Johnson, Kingston, Liberty, Richwoods, Union, and Walton. Reliable per-township 2020 population and settlement data was not available, so no township-by-township table is published here.
ZIP Codes
- 63664 — Potosi (also serves most of the county’s unincorporated core)
- 63631 — Caledonia
Most other unincorporated communities share a ZIP code with the nearest post office town rather than carrying their own.
Geography
Washington County sits in the Ozark foothills, drained by the Big River, Courtois Creek, and Mineral Fork. The terrain is hilly and heavily wooded, shaped by more than a century of lead and barite mining that left the region pocked with old shafts, tailings piles, and mining-camp place names. A portion of the Mark Twain National Forest lies within the county. It borders Franklin County to the north, Jefferson County to the northeast, St. Francois County to the east, Iron County to the south, and Crawford County to the west.
Demographics
Washington County had 23,514 residents at the 2020 census. Potosi and Caledonia are among its largest communities; Caledonia recorded 131 residents in 2020. Household income in the county has historically run below the Missouri median of $68,545, reflecting the decline of large-scale mining employment since the mid-20th century. Population density is roughly 31 people per square mile, one of the more sparsely settled counties in eastern Missouri.
Economy & Local Life
Mining built Washington County — lead first, then barite (“tiff”) through much of the 20th century — and the industry’s legacy shapes the local economy and landscape even after most large operations closed. Corrections and government employment are now significant, anchored by the Potosi Correctional Center, a maximum-security state prison just outside the county seat. Farming, timber, and small manufacturing round out the base, and Terre du Lac draws seasonal and retiree residents around its private lake.
History
Washington County was organized on August 21, 1813, one of Missouri’s original counties, and named in honor of George Washington. Its French-colonial roots predate American organization by a century: French miners worked lead deposits around Old Mines and Mine La Motte-adjacent camps from the early 1700s, and the county remains one of the few places in the United States where a distinct dialect of French, sometimes called “Paw-Paw French,” survived into the modern era. Potosi, platted in the early 1800s and named for the silver-mining city in Bolivia, grew as the county’s administrative and commercial center as lead and later barite mining expanded through the 19th and 20th centuries.
Getting There
Missouri Routes 8, 21, 32, 47, 104, and 185 cross the county; Route 21 is the main north–south corridor linking Potosi to the St. Louis metro area.
- Farmington — about 20 miles south
- Festus — about 30 miles northeast
- St. Louis — about 70 miles northeast
- Rolla — about 45 miles southwest
The nearest commercial airport is St. Louis Lambert International Airport.
Frequently Asked Questions
Where is Washington County, Missouri?
It is in the south-eastern Ozark foothills of Missouri, roughly 70 miles south of St. Louis.
What is the population of Washington County?
23,514, per the 2020 census.
How big is Washington County?
762 square miles (1,970 km2), of which about 2.6 square miles is water.
What is the county seat of Washington County?
Potosi is the county seat.
How many towns are in Washington County?
Two incorporated cities (Potosi and Irondale), two villages (Caledonia and Mineral Point), one census-designated place (Terre du Lac), and dozens of unincorporated communities.
What ZIP codes are in Washington County?
Potosi uses 63664 and Caledonia uses 63631; most other communities share a ZIP with their nearest post office town.
Why is Old Mines significant?
It is the county’s oldest settlement, founded by French lead miners in the early 1700s, and remains linked to Missouri’s historic “Paw-Paw French” dialect community.
More counties in this state: Towns and villages in Missouri.