What is the largest city in St. Clair County, IL?

Belleville is the largest city or town in St. Clair County, with about 41,370 residents.

How many ZIP codes are in St. Clair County?

St. Clair County includes 26 ZIP Code Tabulation Areas, including 62059, 62201, 62203, 62204, 62205.

What is the population of St. Clair County, IL?

About 253,694 people live in St. Clair County, based on American Community Survey 5-year estimates.

What counties border St. Clair County?

St. Clair County borders St. Louis County, MO, St. Louis city, MO, Madison County, Clinton County, Monroe County, Randolph County, Washington County.

St. Clair County, IL: Cities, ZIP Codes & Local Data

Population

253,694

Land area

658sq mi

People per sq mi

386

ZIP codes

26

St. Clair County at a glance

St. Clair County is 69% denser than Illinois as a whole.
By population, it ranks 9th among 102 counties in Illinois.
The median household income is $73,854, 11% below the Illinois median of $83,390.
A typical owner-occupied home is valued at $180,300 (32% below Illinois) and median rent is $1,090 a month.
Its largest cities are Belleville (41,370), O'Fallon (32,262) and East St. Louis (17,999).

Local data for St. Clair County, IL

Counts from official public data

Housing and community stats

St. Clair County, IL, American Community Survey 2020-2024

Full profile

Median household income

$73,854

Poverty rate

13.6%

Median home value

$180,300

Prices +5.3% in a year

Median rent

$1,090/mo

Homeownership

68.4%

Bachelor's or higher

31.8%

Median age

39.9

Average commute

24.0 min

Largest reported origins and ancestries: German Americans (54,517), Irish Americans (24,556), Mexican Americans (8,043).

Home values and rents Income, education and commute

Economy and federal money

Jobs, income, federal spending and pandemic loans

Details

Unemployment rate

3.9%

Aug 2026, -1.0 pts in a year

Average annual pay

$59,034

89,192 jobs, 2025

Income per person

$61,712

BEA, 2024

Federal spending

$2.61B

FY 2026, $10,147 per person

PPP loans

$472M

8,234 loans, 52,623 jobs reported

Campaign donations

$1.04M

Itemized, 2026 cycle

Economy Federal spending PPP loans

How people get to work

St. Clair County, IL, workers 16 and older. American Community Survey 5-year estimates

Drove alone75.4%
Carpooled8.1%
Public transit1.6%
Walked1.5%
Bicycle0.1%
Taxi, ride-hailing, motorcycle or other1.0%
Worked from home12.4%

Average one-way commute: 24.0 minutes for people who do not work from home.

Environment and hazard risk

St. Clair County, IL, from FEMA, NOAA and EPA

Full report

Natural hazard risk

Relatively High

Top: heat wave

Storm events since 1996

829

Most often thunderstorm wind

Flood insurance policies

1,007

1.0% of homes, county

July high / Jan low

90° / 24°F

43.4 inches of rain a year

Hazards, floods and storm history Check a flood zone 18 historic places

Health statistics

Share of adults in St. Clair County, IL, CDC PLACES estimates

All 40 measures

Obesity

38.8%

U.S. 33.3% +5.5 pts

Diabetes

13.1%

U.S. 12.1% +1.0 pts

Smoking

14.2%

U.S. 12.8% +1.4 pts

Uninsured (18-64)

7.8%

U.S. 11.1% -3.3 pts

Cities, towns and ZIP codes in St. Clair County

Population shown

Frequently asked questions

What is the largest city in St. Clair County, IL?: Belleville is the largest city or town in St. Clair County, with about 41,370 residents.
How many ZIP codes are in St. Clair County?: St. Clair County includes 26 ZIP Code Tabulation Areas, including 62059, 62201, 62203, 62204, 62205.
What is the population of St. Clair County, IL?: About 253,694 people live in St. Clair County, based on American Community Survey 5-year estimates.
What counties border St. Clair County?: St. Clair County borders St. Louis County, MO, St. Louis city, MO, Madison County, Clinton County, Monroe County, Randolph County, Washington County.