St. Clair County leans slightly Democratic by roughly 12 points: about 56% of voters vote Democratic and 44% Republican.
About 73% of adults in St. Clair County typically vote, above the U.S. average of about 62%. Among adults in St. Clair County, ~41% vote Democratic, ~32% Republican, and ~27% don't vote. The map below shows estimated turnout by block group.
How St. Clair County compares
Among counties within 50 miles, St. Clair County leans more Democratic than 12 of 14 neighbors.
Politically, St. Clair County sits close to the rest of Illinois.
Politics vary noticeably by city within St. Clair County. The northwest side runs the most Democratic (D+77) and the southwest side runs the most Republican (R+39), a spread of about 116 points.
Why St. Clair County leans the way it does
This analysis examined 14,881 data points per county to find what predicts political lean and turnout. The items below are a few correlations that stood out for St. Clair County, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 65% of residents in St. Clair County live in densely developed areas, about 28 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and St. Clair County sits in the top quarter (about 32%, above 80% of counties). A high never-married share predicts Democratic voting, and about 34% of adults in St. Clair County have never been married, above 82% of counties.
Walkability and Democratic lean
Places with a highly walkable street grid tend to lean Democratic; St. Clair County, IL sits in the top tenth nationally on this measure. A walkable street grid does not change how people vote; it mostly reflects how urban a place is.
Why turnout in St. Clair County looks the way it does
Turnout in St. Clair County sits close to the national pattern. Routine healthcare access, homeownership, education, and food security all land near their national averages here. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- St. Louis City, MO D+65
- Monroe County, IL R+39
- Madison County, IL R+11
- St. Louis County, MO D+28
- Clinton County, IL R+47
- Jefferson County, MO R+39
- Washington County, IL R+53
- Randolph County, IL R+45
- Bond County, IL R+39
- St. Charles County, MO R+14
Counties with Similar Populations
- Yakima County, WA R+6
- Jefferson County, TX D+8
- Cumberland County, PA R+9
- McLennan County, TX R+19
- Harford County, MD R+4
- Clay County, MO R+7
- Kalamazoo County, MI D+17
- Weber County, UT R+21
- Marin County, CA D+48
- Forsyth County, GA R+22
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Sources and methodology
Precinct-level voting records used to fit the model come from Illinois State Board of Elections, distributed by the Voting and Election Science Team. Demographic inputs come from the U.S. Census Bureau (ACS 5-year estimates and the 2020 Decennial Census). Health and environmental inputs come from the CDC (PLACES and the Environmental Justice Index). Land cover comes from the USGS and EPA. Election-day and lead-up weather come from PRISM 4km daily grids and the NOAA Global Historical Climatology Network. Mail-voting and election-administration patterns come from the MIT Election Lab's Survey of the Performance of American Elections. Block-group crime detail comes from CrimeGrade. Internet data and modeling support provided by ISPreports.org.
Modeling and analysis by the BestNeighborhood data science team. Full methodology and findings: political spectrum map.
Methodology reviewed by the BestNeighborhood data team. Last updated May 2026.