St. Charles County, Missouri

St. Charles County is a county in Missouri, United States, about 25 miles northwest of downtown St. Louis on the north bank of the Missouri River. It had a population of 405,262 at the 2020 census, an estimated 426,499 by 2025, and covers 560 square miles (1,450 km2) centred near 38°45′N 90°37′W.

St. Charles is the county seat; its postal code is 63301. The county holds 12 cities, 5 villages and one census-designated place, with no functioning civil townships, and it runs on Central time. Its FIPS code is 29183.

Towns & Villages in St. Charles County

St. Charles County has 18 named places: 12 cities (including the seat), 5 legally incorporated villages, and the census-designated place of Defiance. Missouri law classifies the smaller incorporated places as villages rather than towns; the table below labels them “Town” to keep the Type column consistent with every other state’s page on this site.

Two pairs on that list confuse newcomers. Weldon Spring (5,326 people, home to the former federal uranium-processing site) and Weldon Spring Heights (93 people, a separate incorporated village a few miles south) are distinct municipalities that share only a name. Lake Saint Louis, the city, takes its name from the two private lakes its 1960s developer built; it has no boundary with the city of St. Louis, which sits in a different county entirely. Foristell’s population figure above is the whole city; part of it lies across the line in Warren County and attends the Wright City school district instead of Wentzville’s.

ZIP Codes

• 63301 — St. Charles
• 63304 — St. Peters/Cottleville area
• 63332 — Augusta
• 63341 — Defiance
• 63348 — Foristell
• 63366 — O’Fallon and St. Paul
• 63367 — Lake Saint Louis
• 63368 — O’Fallon and Dardenne Prairie
• 63373 — Portage des Sioux
• 63376 — St. Peters
• 63385 — Wentzville and Flint Hill
• 63386 — West Alton

Cottleville, Weldon Spring, New Melle, Josephville and Weldon Spring Heights have no ZIP code of their own; the Postal Service never opened a dedicated post office in any of them, so mail there is addressed through a neighboring town’s code instead.

Geography

The county occupies the wedge of land between the Missouri and Mississippi Rivers, which meet at its northeastern tip near West Alton. The terrain rolls from river-bottom floodplain in the north and east to gently hilly upland prairie toward the west, where Dardenne Prairie and New Melle sit. The largest bodies of water are the two private lakes that give Lake Saint Louis its name, plus the Missouri River itself, which forms the county’s entire southern boundary.

St. Charles County borders Lincoln County to the northwest, Calhoun County and Jersey County, Illinois to the north and northeast across the Mississippi, Madison County, Illinois to the east, St. Louis County to the southeast, Franklin County to the south, and Warren County to the west.

Demographics

The county had 405,262 residents at the 2020 census, Missouri’s third-highest county total, and an estimated 426,499 by 2025. O’Fallon (91,316) and St. Charles (70,493) are the two largest communities. Median household income was $104,692 in 2024, more than $38,000 above Missouri’s statewide median of roughly $66,000, making St. Charles the wealthiest county in the state by that measure. Population density works out to about 724 people per square mile of land.

Economy & Local Life

Health care and social assistance is the largest employment sector, with 29,262 workers, followed by manufacturing (28,248) and retail trade (24,881). General Motors’ Wentzville Assembly plant, which builds full-size vans and pickups, employs about 3,399 people and is the county’s single largest private employer. St. Peters is the retail hub, anchored by Mid Rivers Mall and Barnes-Jewish St. Peters Hospital, the county’s second-busiest medical center. Lindenwood University, founded in St. Charles in 1827, is the second-oldest institution of higher education west of the Mississippi River. St. Charles hosts the annual Festival of the Little Hills each August in its historic Main Street district; Augusta, home to the first federally recognized American Viticultural Area in the country, anchors the county’s wine-tourism trade along the Missouri Rhineland.

History

French-Canadian fur trader Louis Blanchette founded the settlement as Les Petites Côtes (“the Little Hills”) around 1769; it was renamed for Saint Charles Borromeo and the county was organized on October 1, 1812. The city of St. Charles served as Missouri’s first state capital from 1821 to 1826, while a permanent capitol was built in Jefferson City. The Lewis and Clark Expedition made its final stop in St. Charles in May 1804 before launching upriver the next day. Frontiersman Daniel Boone spent his last years near what is now Defiance; the Daniel Boone Home and Boonesfield Village there preserve the site. A less celebrated chapter unfolded at Weldon Spring: the U.S. Army built the country’s largest TNT and DNT plant there during World War II, and the Atomic Energy Commission later ran a uranium-ore processing plant on the same ground until 1966. The site was contaminated with more than 1.5 million cubic yards of radioactive and asbestos-laden rubble; the Department of Energy completed a cleanup and capped it under a 45-acre engineered mound by 2001.

Getting There

Interstates 70 and 64 both cross the county, along with U.S. Routes 40, 61 and 67 and Missouri Routes 79, 94, 364 and 370. No Amtrak line runs through St. Charles County; the nearest station is St. Louis’s Gateway Station, about 25 miles southeast.

• St. Louis, Missouri — 25 miles southeast
• Columbia, Missouri — 100 miles west
• Jefferson City, Missouri — 110 miles southwest
• Alton, Illinois — 20 miles northeast

Lambert–St. Louis International Airport is the nearest major commercial airport, roughly 15 miles from O’Fallon and St. Peters via I-70.

Frequently Asked Questions

Where is St. Charles County, Missouri?
It sits in eastern Missouri between the Missouri and Mississippi Rivers, about 25 miles northwest of St. Louis, forming part of the St. Louis metropolitan area.

What is the population of St. Charles County?
The county had a population of 405,262 at the 2020 census, an estimated 426,499 by 2025, making it Missouri’s third-most-populous county.

How big is St. Charles County?
It covers 560 square miles (1,450 km2) of land, plus another 32 square miles of water where the Missouri and Mississippi Rivers run along its borders.

What is the county seat of St. Charles County?
St. Charles is the county seat and the largest city founded before the 19th century, though O’Fallon has since surpassed it in population.

How many towns and villages are in St. Charles County?
There are 18 named places: 12 cities, 5 incorporated villages, and the census-designated place of Defiance.

What ZIP codes are in St. Charles County?
Twelve ZIP codes cover the county, from 63301 in St. Charles to 63386 in West Alton; five of the smallest places share a neighboring town’s code.

What historic site is in Defiance?
The Daniel Boone Home and Boonesfield Village mark where frontiersman Daniel Boone lived out his final years, and the Katy Trail, a Missouri state park trail, runs through the community along the Missouri River.

More counties in this state: Towns and villages in Missouri.