Jefferson County, Missouri

Jefferson County is a county in Missouri, United States, about 30 miles south of St. Louis along
the Mississippi River. It had a population of 226,739 at the 2020 census, an estimated 233,132 by
2025, and covers 657 square miles (1,700 km2) of land plus 7.7 square miles (20 km2) of water,
centred near 38°16′N 90°32′W.

Hillsboro is the county seat; its postal code is 63050. The county holds 11 cities, 5 villages
and dozens of smaller unincorporated communities spread across 8 legacy townships, and it runs on
Central Time. Its FIPS code is 29099.

Towns & Villages in Jefferson County

Jefferson County has 16 incorporated places on record: 11 cities and 5 villages, a distinct
Missouri municipal category with its own charter but a smaller population threshold than a city.
Beyond these, the U.S. Census Bureau separately tracks 10 unincorporated CDPs (census designated
places, communities with no local government but a recognizable population cluster) and Wikipedia
names another 39 smaller unincorporated hamlets and crossroads with no population figures of their
own.

Eureka’s 11,646 residents are counted citywide; the city sits mainly in St. Louis County,
with only a small southern edge of its limits reaching into Jefferson County. Herculaneum was the
county’s first seat from 1818 to 1839, before the honor passed to Hillsboro.

The Census Bureau also tracks 10 unincorporated CDPs, ranked here by 2020 population:

Beyond the cities, villages and CDPs above, Wikipedia’s gazetteer for the county names 39
smaller unincorporated communities with no census population of their own: Antonia, Bailey, Belews
Creek, Bushburg, Byrnesville, Danby, Dittmer, Donnell, Fletcher, Flucom, Frumet, Goldman,
Grubville, Hematite, House Springs, Jarvis, Knorpp, Liguori, Local, Ludwig, Mapaville, Melzo,
Meramec Heights, Morse Mill, Munsons, Oermann, Old Mines, Papin, Plattin, Regina, Riverside, Rush
Tower, Seckman, Selma, Sulphur Springs, Valles Mines, Victoria, Vineland and Ware. Most are rural
crossroads or former mining camps; mail there is delivered under the nearest incorporated town or
CDP’s ZIP rather than a code of their own.

Townships

Missouri’s townships are legacy census subdivisions with no governing function today —
the state abolished township government outside a handful of counties decades ago, and none of
Jefferson County’s 8 survive as active local governments. The Census Bureau still uses them
to organize population counts.

ZIP Codes

• 63010 — Arnold
• 63028 — Festus
• 63025 — Eureka (shared with St. Louis County)
• 63020 — De Soto (also serves Olympian Village, Summer Set and Briarwood Estates)
• 63070 — Pevely (also serves Horine)
• 63019 — Crystal City
• 63048 — Herculaneum
• 63050 — Hillsboro (also serves Raintree Plantation)
• 63051 — Byrnes Mill
• 63053 — Kimmswick
• 63069 — LaBarque Creek and Lake Tekakwitha
• 63026 — Murphy
• 63012 — Barnhart
• 63052 — Imperial
• 63049 — High Ridge (also serves Parkdale and Peaceful Village)
• 63016 — Cedar Hill

Cedar Hill Lakes and Scotsdale have no ZIP code of their own on record; mail there is delivered
under a neighboring town’s code.

Geography

Jefferson County sits where the eastern edge of the Ozark Plateau meets the Mississippi River
floodplain, giving it a split character: rolling St. Louis suburbs along the Meramec River in the
north around Arnold and Eureka, and hillier, more rural Ozark-fringe terrain toward the south and
west around De Soto and Old Mines. Of the county’s 664.7 square miles, 657 are land and 7.7
are water, about 1.2 percent — mostly the Mississippi River itself, which forms the
county’s entire eastern border, plus the Big River, Joachim Creek and Plattin Creek, which
drain the interior toward the Mississippi.

St. Louis County lies to the north, Monroe County, Illinois, across the Mississippi River to the
east, Ste. Genevieve County to the southeast, St. Francois County to the south, Washington County
to the southwest, and Franklin County to the west. St. Louis County, Ste. Genevieve County, St. Francois County, Washington County and Franklin County all border
Jefferson directly.

Demographics

Jefferson County had a population of 226,739 at the 2020 census, the sixth-highest county total
in Missouri, and the latest estimate puts it near 233,132 residents by 2025. Arnold and Festus are
the two largest communities, together holding well over a tenth of the county’s population.
Median household income runs about $82,851 (2024 ACS estimate), noticeably higher than the
Missouri median household income of $68,545 (2023 ACS). Population density works out to roughly
345 people per square mile of land, concentrated heavily in the northern suburbs closest to St.
Louis.

Economy & Local Life

Health care and social assistance is the county’s largest employment sector, about 17,678
workers, followed by manufacturing at 14,478 and retail trade at 13,650. Arnold is home to an
Anheuser-Busch InBev metal-container plant that the company describes as the largest can
manufacturing facility in the country, a major manufacturing employer in the northern part of the
county. Herculaneum’s Doe Run Company still runs lead-refining operations on the site of its
former smelter, though the smelter itself closed at the end of 2013. Hillsboro is home to Jefferson
College, a public community college founded in 1963 that serves the whole county. The county’s
biggest annual event is Kimmswick’s Apple Butter Festival at the end of October, which
typically draws more than 100,000 visitors to the small river town for two weekends of vendors and
live entertainment.

History

The Missouri legislature organized Jefferson County on 8 December 1818, naming it for former
president Thomas Jefferson. Moses Austin and Samuel Hammond had already founded Herculaneum a
decade earlier, in 1808, as a shipping point for lead mined nearby; the town took its name from the
ancient Roman city buried by Mount Vesuvius, chosen because its limestone river bluffs resembled
amphitheater seats. Herculaneum served as the new county’s first seat, but the seat moved to
the more central Hillsboro in 1839 after the railroad bypassed the river town and its influence
faded.

Lead defined much of the county’s economy for two centuries. French colonists began mining
lead around Old Mines in the early 18th century, working what became known as the richest galena
deposit in the country; the community kept a distinct French Creole culture and its own Missouri
French dialect well into the 20th century. The St. Joseph Lead Company revived Herculaneum’s
industry starting in 1887, and by 1892 its smelters were producing roughly 225,000 tons of refined
lead a year, the largest such operation in the nation. The Doe Run Company took over the plant in
1981. In August 2001, city officials found lead dust on Herculaneum’s roads at levels far
above hazardous thresholds, and a 2010 EPA settlement cost Doe Run $65 million in fines and $7
million in civil penalties; the smelter stopped operating on 31 December 2013 and was demolished in
2018.

In 1980, the U.S. census found that Jefferson County held the mean center of the United States
population — the first time that point had ever been recorded west of the Mississippi
River.

Getting There

Interstate 55 runs along the county’s eastern side through Arnold, Pevely, Festus and
Crystal City. Missouri Routes 21, 30, 109, 110, 141 and 231 carry most of the remaining traffic; no
interstate crosses the county’s hillier western and southern half.

• St. Louis — about 30 miles north
• Farmington — about 35 miles south
• Union — about 25 miles west
• Sainte Genevieve — about 30 miles southeast

St. Louis Lambert International Airport, roughly 30 miles north of Hillsboro, is the nearest
major commercial airport. Amtrak has no station in Jefferson County; the closest stop is Kirkwood,
in St. Louis County, served by the Texas Eagle and Missouri River Runner lines.

Frequently Asked Questions

Where is Jefferson County located?
It sits in eastern Missouri along the Mississippi River, about 30 miles south of St. Louis, bordered
by St. Louis, Ste. Genevieve, St. Francois, Washington and Franklin counties, plus Monroe County,
Illinois, across the river.

What is the population of Jefferson County?
226,739 at the 2020 census, with a 2025 estimate near 233,132.

How big is Jefferson County?
657 square miles (1,700 km2) of land plus 7.7 square miles (20 km2) of water, 664.7 square miles in
total.

What is the county seat of Jefferson County?
Hillsboro, which took over from the original seat, Herculaneum, in 1839.

How many towns and cities are in Jefferson County?
16 incorporated places — 11 cities and 5 villages — plus 10 unincorporated CDPs and 39
smaller named communities with no population count of their own.

What ZIP codes does Jefferson County use?
Sixteen, led by 63010 (Arnold), 63028 (Festus), 63020 (De Soto) and 63050 (Hillsboro); the full list
is in the ZIP Codes section above.

What is Jefferson County known for?
Two centuries of lead mining and smelting around Herculaneum and Old Mines, holding the U.S. mean
center of population in 1980, and Kimmswick’s Apple Butter Festival each October.

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