Illinois leans Democratic by roughly 16 points: about 58% of voters vote Democratic and 42% Republican.
About 67% of adults in Illinois typically vote, near the U.S. average of about 62%. Among adults in Illinois, ~39% vote Democratic, ~28% Republican, and ~33% don't vote. The map below shows estimated turnout by block group.
How Illinois compares
Among states within 500 miles, Illinois is the most Democratic-leaning.
Politics vary noticeably by county within Illinois. The northeast side runs the most Democratic (D+39) and the southeast side runs the most Republican (R+49), a spread of about 88 points.
Why Illinois leans the way it does
This analysis examined 14,881 data points per state to find what predicts political lean and turnout. The items below are a few correlations that stood out for Illinois, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 78% of residents in Illinois live in densely developed areas, about 42 points above the U.S. average of 36%. A high never-married share predicts Democratic voting, and about 36% of adults in Illinois have never been married, above 84% of states.
Paved land cover and Democratic lean
Places with extensive paved surfaces tend to lean Democratic; Illinois sits in the top tenth nationally on this measure. Paved ground does not change how people vote; it mostly reflects how urban and built-up a place is.
Why turnout in Illinois looks the way it does
Turnout in Illinois 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 States
States with Similar Populations
- Pennsylvania Even
- Ohio R+8
- Georgia D+4
- North Carolina Even
- Michigan D+2
- New Jersey D+11
- Virginia D+10
- Washington D+16
- Arizona Even
- Massachusetts D+26
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.