St. Clair County, Illinois
Located in Illinois, St. Clair County has a population of 253,694 residents and a median age of 39.9 years, making it the #284 most populous county out of 3,222 nationwide. In terms of economic indicators, the county has a poverty rate of 13.6%. The median home value is $180,300, and the median household income is $73,854, which is 2% below the national median.
Demographics
St. Clair County has a population of 253,694, making it the #284 most populous county in the US. The median age is 39.9 years, which is 2.6% above the national median.
Population Trend
Rankings →Year-over-Year Population Growth
Age & Sex Distribution
Race & Ethnicity
Nativity
Geographic Mobility (Past Year)
Economy
The median household income in St. Clair County is $73,854, ranking #926 out of 3,222 counties — 1.7% below the national median. The poverty rate is 13.6% and unemployment stands at 5.8%.
Median Household Income Trend
Rankings →Income Distribution
Industry of Employment
Occupation
Housing
The median home value in St. Clair County is $180,300 (-36.0% vs national). Renters pay a median of $1,090/mo and the homeownership rate is 68.4%.
Median Home Value Trend
Rankings →Household Type
Education
In St. Clair County, 31.8% of adults age 25+ hold a bachelor's degree or higher, which is 5.6% below the national average, ranking #640 out of 3,222 counties.
Bachelor's Degree or Higher Trend
Rankings →Health & Wellbeing
Life expectancy in St. Clair County is 74.1 years. 17.6% of adults report poor or fair health and 5.3% lack health insurance. Data from County Health Rankings (2025).
Life Expectancy Trend
Substance Use
16.3% of adults in St. Clair County smoke , 38.2% are obese , and 20.0% report excessive drinking. The drug overdose death rate is 36.0 per 100,000.
Adult Smoking Trend
Safety
The homicide rate in St. Clair County is 18.2 per 100,000 and the suicide rate is 11.2 per 100,000. Motor vehicle deaths occur at a rate of 14.7 per 100,000.
Homicide Rate Trend
Families & Children
17.3% of children in St. Clair County live in poverty and the infant mortality rate is 9.3 per 1,000 live births. The teen birth rate is 18.8 per 1,000 females age 15–19.
Infant Mortality Trend
Civic & Transportation
Voter turnout in St. Clair County is 65.3%. The mean commute time is 26.2 min, which is 5.2% below the national average.
Voter Turnout Trend
Mean Commute Time Trend
Rankings →Elections
In the 2024 presidential election, St. Clair County voted Democratic with a margin of 7.9%. The vote was 53% Dem / 45.1% Rep. Compared to 2020, the margin shifted 0.8 toward Republicans .
Vote Share Over Time
About St. Clair County, Illinois
St. Clair County, Illinois has a total population of 253,694, making it the 284th most populous county in the United States. The median age in St. Clair County is 39.9 years, which is 2.6% above the national median of 38.9 years.
The median household income in St. Clair County is $73,854, which ranks #926 of 3,222 counties nationwide. This is 1.7% below the national median of $75,149. The poverty rate is 13.6%, higher than the national rate of 12.6%. The unemployment rate stands at 5.8%.
The median home value in St. Clair County is $180,300, 36.0% below the national median. Renters in St. Clair County pay a median gross rent of $1,090 per month. The homeownership rate is 68.4%, compared to the national rate of 64.4%.
In St. Clair County, 31.8% of residents aged 25 and older hold a bachelor's degree or higher, 5.6% below the national average of 33.7%. Health insurance coverage stands at 94.9% of the population. The average commute time for workers is 26.2 min.
St. Clair County is a diverse community. The largest racial or ethnic group is White (non-Hispanic) at 59.1% of the population, followed by Black (non-Hispanic) (27.7%) and Two or More Races (5.8%).
All data for St. Clair County, Illinois comes from the U.S. Census Bureau's American Community Survey (ACS) 5-Year Estimates. These figures are estimates based on survey sampling and are subject to margin of error. For the most detailed and up-to-date data, visit the Census Bureau's official data portal.