Jefferson County leans heavily Republican by roughly 44 points: about 28% of voters vote Democratic and 72% Republican.
About 70% of adults in Jefferson County typically vote, above the U.S. average of about 62%. Among adults in Jefferson County, ~20% vote Democratic, ~50% Republican, and ~30% don't vote. The map below shows estimated turnout by block group.
How Jefferson County compares
Among counties within 50 miles, Jefferson County leans more Republican than 3 of 15 neighbors.
Jefferson County runs about 55 points more Republican than Illinois as a whole. Illinois leans Democratic overall, while Jefferson County is one of the few Republican-leaning pockets.
Politics vary noticeably by city within Jefferson County. The southeast side is the most Republican-leaning (R+65) and the west side is the least Republican-leaning (R+40), a spread of about 25 points.
Why Jefferson 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 Jefferson County, not a ranked or complete list of what matters most.
Jefferson County votes against the grain of Illinois. Illinois leans Democratic overall, while Jefferson County runs about 55 points more Republican. Car-dependent areas vote Republican, and about 83% of residents in Jefferson County drive to work alone, above 86% of counties.
Park access and Republican lean
Places with low park coverage tend to lean Republican; Jefferson County, IL sits in the bottom quarter nationally on this measure. Park access does not change how people vote; it tends to track denser, higher-income areas.
Why turnout in Jefferson County looks the way it does
Turnout in Jefferson 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
- Marion County, IL R+47
- Franklin County, IL R+52
- Hamilton County, IL R+62
- Washington County, IL R+53
- Wayne County, IL R+65
- Perry County, IL R+49
- Clay County, IL R+63
- Clinton County, IL R+47
- Williamson County, IL R+36
- White County, IL R+59
Counties with Similar Populations
- Calloway County, KY R+36
- Williams County, OH R+50
- Green County, WI R+11
- Albany County, WY D+12
- Dodge County, NE R+31
- Macon County, NC R+42
- Yadkin County, NC R+61
- Webster County, IA R+22
- Clarion County, PA R+50
- Clark County, KY R+39
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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.