Jersey County leans heavily Republican by roughly 44 points: about 28% of voters vote Democratic and 72% Republican.
About 83% of adults in Jersey County typically vote, above the U.S. average of about 62%. Among adults in Jersey County, ~23% vote Democratic, ~60% Republican, and ~17% don't vote. The map below shows estimated turnout by block group.
How Jersey County compares
Among counties within 50 miles, Jersey County leans more Republican than 10 of 17 neighbors.
Jersey County runs about 55 points more Republican than Illinois as a whole. Illinois leans Democratic overall, while Jersey County is one of the few Republican-leaning pockets.
Politics vary noticeably by city within Jersey County. The northeast side is the most Republican-leaning (R+54) and the south side is the least Republican-leaning (R+35), a spread of about 19 points.
Why Jersey 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 Jersey County, not a ranked or complete list of what matters most.
Jersey County votes against the grain of Illinois. Illinois leans Democratic overall, while Jersey County runs about 55 points more Republican.
High-school completion, uninsured rate, and voter turnout
Places that combine high-school-completion-heavy adults and a low uninsured rate tend to turn out at a higher rate, as Jersey County, IL does.
Why turnout in Jersey County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Jersey County is in the top quarter nationally for routine-care measures such as insurance coverage, preventive screenings, and dental visits. The dental-visit rate here is about 65%, about 5 points above the U.S. average of 60%. Homeowners vote more often than renters, and about 80% of households in Jersey County own their home, above 80% of counties. High high-school completion lines up with higher turnout, and about 94% of adults in Jersey County have completed high school, above 85% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Calhoun County, IL R+56
- Greene County, IL R+56
- Macoupin County, IL R+42
- Madison County, IL R+11
- St. Charles County, MO R+14
- St. Louis County, MO D+28
- St. Louis City, MO D+65
- Lincoln County, MO R+51
- Scott County, IL R+64
- St. Clair County, IL D+13
Counties with Similar Populations
- Sevier County, UT R+70
- Logan County, CO R+50
- Fayette County, IL R+59
- Hockley County, TX R+63
- Letcher County, KY R+65
- Hertford County, NC D+25
- Scott County, VA R+70
- Clark County, AR R+18
- Dakota County, NE R+15
- Stutsman County, ND R+34
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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.