Jefferson County, Illinois

Jefferson County is a county in Illinois, United States, in the region known locally as
Little Egypt, about 74 miles west of St. Louis, Missouri. It had a population of 37,113 at the
2020 census, an estimated 36,147 by 2025, and covers 584 square miles (1,510 km2), of which 571
square miles (1,480 km2) are land, centred near 38°18′N 88°55′W.

Mount Vernon is the county seat and the county’s largest city; its postal code is 62864. The
county holds 3 cities, 7 incorporated villages, 1 census-designated place and 24 unincorporated
communities across 16 townships, and it runs on Central Time. Its FIPS code is 17081.

Towns & Villages in Jefferson County

Jefferson County has 35 named places on record: 3 cities (one the county seat), 7 incorporated
villages, 1 census-designated place and 24 unincorporated communities with no local government of
their own. CDP stands for census designated place; Unincorp. covers crossroads and rural
communities with no formal boundary.

Three places on this list straddle boundaries. Centralia’s population figure above is
citywide — the largest portion of the city sits in Marion County, with smaller slices
reaching into Jefferson, Clinton and Washington counties. Waltonville sits at the meeting point
of four townships (Bald Hill, Blissville, Elk Prairie and McClellan), so its village limits cross
township lines rather than sitting inside one. Nason, at 199 residents, is the least populous
incorporated city in Illinois and shares its 62816 ZIP with neighboring Bonnie rather than
carrying one of its own.

Townships

Jefferson County’s 16 townships range from Mount Vernon Township, which contains most of the
county seat, to rural Moore’s Prairie Township with no incorporated community of its own.

ZIP Codes

• 62864 — Mount Vernon (the county’s most populous ZIP)
• 62846 — Ina
• 62814 — Bluford
• 62898 — Woodlawn
• 62830 — Dix
• 62816 — Bonnie (also serves Nason, which has no ZIP of its own)
• 62894 — Waltonville
• 62810 — Belle Rive
• 62872 — Opdyke

The county’s 24 unincorporated communities have no ZIP code of their own; mail there is
delivered under the nearest incorporated town’s code. Centralia’s ZIP, 62801, is administered
from Marion County, where most of the city’s population lives, and is not counted among Jefferson
County’s own codes.

Geography

Jefferson County sits in Illinois’s Little Egypt lowlands. Of its 584 square miles, 571 are
land and 13 are water, about 2.2 percent. The Big Muddy River crosses the county’s southern edge
and feeds Rend Lake, an 18,900-acre reservoir the county shares with neighboring Franklin
County — the largest body of water anywhere near Jefferson County.

Marion County lies to the north, Wayne County to the northeast, Hamilton County to the
southeast, Franklin County to the south, Perry County to the southwest, and Washington County to
the west. Marion County,
Wayne County,
Hamilton County,
Franklin County,
Perry County and
Washington County all
border Jefferson directly.

Demographics

Jefferson County had a population of 37,113 at the 2020 census, and the latest estimate puts
the county near 36,147 residents, a slight decline. Mount Vernon and Centralia (its Jefferson
County slice) are the two largest communities. Median household income runs $63,118, well below
Illinois’s 2023 ACS statewide figure of $80,306. Population density works out to roughly 65
people per square mile of land, typical for a rural Little Egypt county built around one
mid-sized city.

Economy & Local Life

Manufacturing employs the most workers in the county, about 2,949 people, followed by health
care and social assistance at 2,600 and retail trade at 2,085. Continental Tire’s Mount Vernon
plant is the county’s single largest private employer, with roughly 3,496 workers as of 2023,
followed by a Walgreens distribution center at 2,138. Good Samaritan Hospital, with about 1,484
employees, and Crossroads Community Hospital anchor health care locally, alongside National
Railway Equipment Company. Rend Lake College and satellite programs from Southeastern Illinois
College and Kaskaskia College run the Southern Illinois Manufacturing Academy, a $5 million
training facility that opened in Mount Vernon in November 2024. The county’s best-known
recurring event is Mount Vernon’s Market Days, held the first Saturday of every month from April
through October in the downtown historic district.

History

The Illinois General Assembly organized Jefferson County in 1819, carving it out of White,
Edwards and Franklin counties, and named it for Thomas Jefferson. Andrew Moore is credited as the
county’s first settler, arriving in 1810, with the first permanent settlement following in 1816.
Zadok Casey founded Mount Vernon in 1817, and the town became the county seat.

In 1848, the Illinois Supreme Court moved its First Grand Division to Mount Vernon, giving the
small county seat an appellate court that operated there for decades. On February 19, 1888, a
tornado tore through Mount Vernon, killing 37 people and destroying more than 450 houses; Clara
Barton personally directed American Red Cross relief efforts in the town afterward, one of the
organization’s early large-scale domestic disaster responses.

Getting There

Interstate 57 and Interstate 64 run concurrently through Mount Vernon on a stack interchange at
the city’s southwest side, the county’s main highway junction. U.S. Route 51 and Illinois Routes
15, 37, 142 and 148 also cross the county.

• Centralia — about 20 miles northwest
• Marion — about 40 miles south
• Carbondale — about 46 miles south
• Effingham — about 59 miles north

Veterans Airport of Southern Illinois, in Marion about 40 miles south, is the nearest airport
with scheduled passenger service, flying daily to Chicago O’Hare on Contour Airlines. MidAmerica
St. Louis Airport, a cargo facility roughly 45 miles away, and Mount Vernon’s own general-aviation
airport handle other air traffic. Amtrak’s City of New Orleans, Saluki and Illini trains stop at
the Centralia station, the nearest passenger rail service to the county.

Frequently Asked Questions

Where is Jefferson County located?
It sits in southern Illinois’s Little Egypt region, about 74 miles west of St. Louis, Missouri,
bordered by Marion, Wayne, Hamilton, Franklin, Perry and Washington counties.

What is the population of Jefferson County?
37,113 at the 2020 census, with a 2025 estimate near 36,147.

How big is Jefferson County?
584 square miles (1,510 km2), of which 571 square miles are land.

What is the county seat of Jefferson County?
Mount Vernon, founded in 1817 by Zadok Casey, is the county seat and largest city.

How many towns and villages are in Jefferson County?
Ten incorporated places — Mount Vernon, Centralia, Nason, Belle Rive, Bluford, Bonnie, Dix,
Ina, Waltonville and Woodlawn — plus the Opdyke CDP and 24 unincorporated communities.

What ZIP codes does Jefferson County use?
62864 for Mount Vernon, 62846 for Ina, 62814 for Bluford, 62898 for Woodlawn, 62830 for Dix,
62816 for Bonnie and Nason, 62894 for Waltonville, 62810 for Belle Rive and 62872 for Opdyke.

What is Jefferson County known for?
The February 1888 Mount Vernon tornado that killed 37 people and drew Clara Barton’s Red Cross to
town, and Rend Lake, the 18,900-acre reservoir it shares with Franklin County.

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