Cook County, IL Political Map | Democrat & Republican Areas in Cook County

By the BestNeighborhood data science team. Last updated May 2026.

Cook County leans heavily Democratic by roughly 42 points: about 71% of voters vote Democratic and 29% Republican.

 

About 59% of adults in Cook County typically vote, near the U.S. average of about 62%. Among adults in Cook County, ~42% vote Democratic, ~17% Republican, and ~41% don't vote. The map below shows estimated turnout by block group.

How Cook County compares

Among counties within 50 miles, Cook County is the most Democratic-leaning.

Cook County runs about 31 points more Democratic than Illinois as a whole.

Politics vary noticeably by city within Cook County. The northeast side runs the most Democratic (D+71) and the southwest side runs the most Republican (R+9), a spread of about 80 points.

Why Cook 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 Cook County, not a ranked or complete list of what matters most.

Dense areas vote Democratic. About 97% of residents in Cook County live in densely developed areas, about 60 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Cook County sits in the top quarter (about 41%, above 93% of counties). A high never-married share predicts Democratic voting, and about 42% of adults in Cook County have never been married, above 95% of counties.

Walkability and Democratic lean

Places with a highly walkable street grid tend to lean Democratic; Cook 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 Cook County looks the way it does

Renters vote less often than owners. About 39% of households in Cook County rent, about 14 points above the U.S. average of 25%. High food insecurity lines up with lower turnout, and about 22% of adults in Cook County report food insecurity, above 81% of counties. Learn more about the findings and methodology on the political spectrum map.

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.