St. Clair County, Illinois Demographics 2026

Population Overview

St. Clair County is located in Illinois with a total population of 254,777. It is the 9th most populous county out of 102 in Illinois. The county encompasses 1 Census-designated place.

Age Demographics

The median age in St. Clair County is 39.5 years. This is 2% higher than the state median of 38.9 years.

Economy, Income & Housing

The median household income in St. Clair County is $70,178. This is 14% lower than the state median of $81,702. Compared to the national median of $78,538, household income here is 11% lower. The poverty rate stands at 13.6%. This is 16% higher than the state poverty rate of 11.7%. The unemployment rate is 5.7%. This is 2% lower than the state rate of 5.8%. The median home value is $168,800. Housing costs are 33% lower than the state median of $250,500. With a home-value-to-income ratio of just 2.4x, St. Clair County is one of the most affordable housing markets in the area. 67.8% of occupied housing units are owner-occupied. This homeownership rate is 1% higher than the state average of 66.8%.

Race & Ethnicity

The largest racial or ethnic group in St. Clair County is White (non-Hispanic), making up 59.5% of the population. Black or African American residents account for 27.8%. The Black or African American population is significantly higher than the state average (27.8% vs 13.6%). The Hispanic or Latino population (5.0%) is well below the state average of 18.5%. The Asian population (1.5%) is well below the state average of 5.8%.

Education

30.7% of residents aged 25 and older hold a bachelor's degree or higher. This is 17% lower than the state rate of 37.2%. Nationally, 35.0% of adults hold at least a bachelor's degree. The high school graduation rate (or equivalent) is 92.7%.