St. Clair County, Illinois Demographics
Population trends, housing costs, income, commuting, and health, all on one page.
St. Clair County, IL Population Density Map and Area Scores
Area Score
Health, income and education, each graded from F to A+. Explore interactive maps for deeper analysis.
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C
Health Below averageLess healthy than 88% of counties in Illinois
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C
Income Below average
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C
Education Below averageBetter educated than 84% of counties in Illinois
Source: Map AI Methodology
Population: density and quick facts
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| Population | 253,661 | 12,692,444 | 337,468,954 |
| Population density (per sq mi) | 376.1 | 219.1 | 86.4 |
| Population growth (%/yr) | -0.60% | -0.16% | 0.59% |
| Median age | 38.8 | 37.4 | 37.3 |
| Households | 100,831 | 5,035,584 | 130,235,071 |
Population in St. Clair County declined by 3.1% from 2009 to 2024, reaching 253,661 in 2024.
Population Growth 2009–2024
Race & Ethnicity
Age & Sex
The largest generation in St. Clair County is Millennials, aged 29–44, at 20.9% of residents. That is 0.9 points below Illinois as a whole.
- Gen Z 13–28 51,734 20.4% -0.9 pts
- Millennials 29–44 53,116 20.9% -0.9 pts
- Gen X 45–60 52,855 20.8% +0.4 pts
- Boomers 61–79 43,844 17.3% +0.4 pts
Residents by birth cohort, from the 2025 age distribution. The right-hand figure is how far each cohort's share sits above or below Illinois, in percentage points. Children younger than Gen Z and the generations before the Boomers are counted in the population but not shown here, so these shares do not add up to 100%.
Male and female share
Women are 51.6% of the people living in St. Clair County and men 48.4%.
- Women 51.6% Illinois 50.6%
- Men 48.4% Illinois 49.4%
How many residents match a customer profile?
Residents matching this profile
100% of everyone living in St. Clair County
Pick an age range and a women/men split and the figure above answers with how many residents that profile reaches.
Economy
St. Clair County has a the economy index of C, which means it is somewhat prosperous.
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| Median household income | $73,876 | $84,042 | $80,455 |
| Income growth (%/yr) | 5.03% | 4.46% | 4.80% |
| Unemployment rate | 5.8% | 5.8% | 5.2% |
The median household income in St. Clair County is about 12% lower than in Illinois.
Housing
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| Median home price | $121,433 | $149,936 | $248,835 |
| Median rent | $1,089 | $1,274 | $1,407 |
| Homeownership rate | 68.4% | 67.1% | 65.2% |
The median home price in St. Clair County is about 9.3 years' worth of rent — buying at the median price costs roughly as much as paying the median rent of $1,089 per month for that long.
Commute Time & Mobility
Commuters in St. Clair County spend about 43 minutes on the road round trip each working day. Over a typical 250-day work year, that adds up to roughly 179 hours, about 7.4 full days, spent commuting.
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| One-way commute (min) | 21.4 | 23.6 | 22.4 |
| Round-trip commute (min) | 42.8 | 47.3 | 44.8 |
| Yearly time spent (hours) | 179 | 197 | 187 |
| Estimated yearly cost | $5,534 | $6,104 | $5,790 |
| Work from home | 12.4% | 15.9% | 15.0% |
| Highway traffic (vehicles/day) | 10,578 | 7,977 | 8,813 |
| Local road traffic (vehicles/day) | 1,794 | 1,547 | 1,355 |
Fastest commutes among counties in
Illinois:
Edgar County (12.0 min), Brown County (12.7 min), Morgan County (13.1 min).
Slowest:
Calhoun County (43.8 min), Pulaski County (31.2 min), Pope County (31.0 min).
The average commute time in St. Clair County is 21 minutes, shorter than the 24 minutes in Illinois.
Estimated yearly cost applies a single national wage rule of thumb (U.S. Bureau of Labor Statistics average hourly earnings), not a measurement of wages in this area. Traffic volume figures come from proprietary Ticon and TrafficZoom data.
Education & Households
St. Clair County has a education index of C, which means it is somewhat educated.
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| Bachelor's degree or higher | 28.2% | 34.1% | 31.6% |
| Average household size | 2.47 | 2.46 | 2.53 |
Highest education index among counties in
Illinois:
DuPage County (0.4), Champaign County (0.4), Lake County (0.4).
Lowest:
Hardin County (0.2), Fayette County (0.2), Perry County (0.2).
Health
St. Clair County has a health index of C, which means it is somewhat healthy.
| Metric | St. Clair County | Illinois Avg | U.S. Average |
|---|---|---|---|
| Life expectancy (years) | 75.9 | 77.9 | 78.3 |
| Self-rated poor health | 18.2% | 15.6% | 16.3% |
| Smokers | 19.3% | 19.2% | 19.0% |
Highest health index among counties in
Illinois:
DuPage County (0.8), Champaign County (0.8), Monroe County (0.8).
Lowest:
Alexander County (0.8), Pulaski County (0.8), Gallatin County (0.8).
St. Clair County, IL Compared With Nearby Counties
St. Clair County, IL is the 2nd largest of the 5 counties compared here, 253,661 residents against a local median of 35,993. St. Clair County, IL's median home price, at $121,433, runs 34% above the $90,789 typical of the counties around it.
The counties themselves spread $158,628 on median home price, so St. Clair County, IL sits at one end of an already wide local range rather than apart from it. St. Clair County, IL has the 2nd highest median home price of the 5 areas compared here.
| Area | Population | Median household income | Median home price | Commute |
|---|---|---|---|---|
| St. Clair County, IL | 253,661 | $73,876 #4/5 | $121,433 #2/5 | 21.4 min #2/5 |
| Monroe County, IL | 35,033 | $103,327 | $208,158 | 28.2 min |
| Madison County, IL | 264,024 | $75,869 | $116,579 | 22.7 min |
| Randolph County, IL | 30,051 | $69,106 | $49,530 | 18.3 min |
| Clinton County, IL | 36,954 | $86,530 | $64,999 | 21.8 min |
Frequently Asked Questions
Common questions about St. Clair County, Illinois.
How many people live in St. Clair County, Illinois?
About 253,661 people live in St. Clair County, Illinois, in 100,831 households of 2.5 people on average. The median age is 38.8, so residents are older than the U.S. median of 37.3 by about 2 years.
Is St. Clair County, Illinois mostly urban or rural?
Averaged over its land area, St. Clair County, Illinois has 376 people per square mile, a density typical of a mix of suburbs, small towns and farmland. That is about 4.4 times the U.S. average of 86.
How affordable is housing in St. Clair County, Illinois?
The median home costs 1.6 times the median household income ($121,433 against $73,876), compared with 3.1 times nationally. That is within the traditional rule of thumb of about 3 times income. Median rent of $1,089 a month takes about 18% of the median household's income, below the 30% level at which HUD considers renters cost-burdened.
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