St. Clair County, Illinois Population 2026
Updated April 2026 · US Census ACS 2023 5-Year Estimates · 9th-largest in Illinois
The population of St. Clair County, Illinois is 254,777 as of the 2023 American Community Survey, making it the 9th-largest county in Illinois. The median household income is $70,178, the median home value is $168,800, and the median age is 39.5.
The population of St. Clair County has declined 7.1% since 2010 (270,368 → 251,149), a -0.53% annualized rate.
254,777
Population
-0.53%
Annual growth
387
People / sq mi
$70,178
Median Income
$168,800
Median Home Value
St. Clair County covers 658 sq mi of land at 387.3 people per square mile.
About St. Clair County, IL
What distinguishes St. Clair County is density: among the most densely settled of US counties, around 387 people per square mile. St. Clair County is a county in Illinois with a population of 254,777. That makes it one of the ten largest counties in Illinois in the country, at #9 by population.
Median household income is $70,178, below the US median of $78,538. The poverty rate is 9.5%, below the national 12.4%. Median home value is $168,800, with typical rent around $1,032.
Educational attainment is on the higher side for US counties — 30.7% of adults hold a four-year degree, below the national 35.0%. A solid 10.9% of workers are based at home, below the national 14.0%, and the average commute runs about 25 minutes each way.
That density explains much of the rest of the profile in St. Clair County: denser places lean toward renting, shorter commutes by transit, and a younger working-age mix.
St. Clair County Population History (2010-2024)
The county of St. Clair County had a population of 270,368 in 2010 and 251,149 in 2024, a -7.1% growth over 14 years. The peak was 270,368 in 2010. Average annual growth rate: -0.52%.
251,149
Population (2024)
270,368
Population (2010)
270,368
Peak (2010)
-0.52%
Avg Annual Growth
| Year | Population |
|---|---|
| 2010 | 270,368 |
| 2011 | 270,097 |
| 2012 | 268,748 |
| 2013 | 266,934 |
| 2014 | 266,061 |
| 2015 | 265,008 |
| 2016 | 263,482 |
| 2017 | 262,881 |
| 2018 | 261,631 |
| 2019 | 259,889 |
| 2020 | 257,070 |
| 2021 | 255,210 |
| 2022 | 252,947 |
| 2023 | 252,094 |
| 2024 | 251,149 |
Race & Ethnicity
| White | 61.2% |
| Black or African American | 28.0% |
| Asian | 0.0% |
| Hispanic or Latino (any race) | 2.3% |
| Two or More Races | 0.0% |
Age & Sex
39.5
Median Age
51.5%
Female
48.5%
Male
16.7%
Age 65+
Age Distribution
Children (under 15): 19.2% · Seniors (65+): 16.7%
Income & Poverty
| Median household income | $70,178$-11,524 vs state |
| Mean household income | $92,847 |
| Per-capita income | $37,824 |
| Poverty rate | 9.5%+1.3% vs state |
| Unemployment rate | 3.5% |
| Employment-to-population | 57.9% |
Top Industries by Employment
The largest employment sector in St. Clair County is professional & business services, accounting for 23.1% of workers.
How residents commute
1.9%
Drive alone
1.5%
Carpool
76.9%
Public transit
10.9%
Work from home
24.7 min
Avg commute
Housing
$168,800$-81,700 vs state
Median home value
$1,032
Median rent
67.8%
Homeownership rate
115,348
Total housing units
87.8%
Occupied
12.2%
Vacant
32.2%
Renter-occupied
Social & access
94.6%
With health insurance
93.3%
With broadband internet
37.6%
Foreign-born
11.8%
Veterans (18+)
15.1%
With a disability
94.7%
Speak language other than English at home
Education
92.7%
High School+
30.7%
Bachelor's+
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County rankings
Frequently Asked Questions
St. Clair County, Illinois has a population of 254,777 according to the US Census Bureau's 2023 American Community Survey 5-year estimates, making it the 9th-largest county in Illinois. Population density is 387 people per square mile.
The population of St. Clair County has declined 7.1% since 2010 (270,368 → 251,149), a -0.53% annualized rate.
The median household income in St. Clair County, Illinois is $70,178, with mean (average) household income of $92,847 and per-capita income of $37,824. 9.5% of residents live below the federal poverty level.
In St. Clair County, the largest racial and ethnic groups are White (61.2%), Black or African American (28.0%), Hispanic or Latino (2.3%). Figures are from the US Census Bureau's 2023 ACS 5-year estimates and reflect self-reported responses.
The median age in St. Clair County, Illinois is 39.5 years. Residents are 51.5% female and 48.5% male.
The median home value in St. Clair County is $168,800 and median monthly rent is $1,032. 67.8% of occupied housing units are owner-occupied. The county has 115,348 total housing units, 12.2% of which are vacant.
The largest employment sector in St. Clair County, Illinois is professional, scientific, and management services, employing 23.1% of workers. The unemployment rate is 3.5%.
Chicago is among the largest cities associated with St. Clair County, Illinois, with a population of 2,707,648.
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Statewide data for Illinois
Population, race, income, age, and trends across Illinois
Data from the American Community Survey (ACS) 5-Year estimates.
Source: U.S. Census Bureau ACS, 2026.