Jefferson County leans heavily Republican by roughly 40 points: about 30% of voters vote Democratic and 70% Republican.
About 79% of adults in Jefferson County typically vote, above the U.S. average of about 62%. Among adults in Jefferson County, ~24% vote Democratic, ~55% Republican, and ~21% 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 6 of 13 neighbors.
Jefferson County runs about 21 points more Republican than Missouri as a whole.
Politics vary noticeably by city within Jefferson County. The south side is the most Republican-leaning (R+54) and the northeast side is the least Republican-leaning (R+30), a spread of about 24 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.
Areas with many family households vote Republican. About 71% of households in Jefferson County are family households, above 84% of counties.
Homeownership and voter turnout
Places with homeowner-heavy households tend to turn out at a higher rate; Jefferson County, MO sits in the top tenth nationally on this measure.
Why turnout in Jefferson County looks the way it does
Homeowners vote more often than renters. About 83% of households in Jefferson County own their home, about 8 points above the U.S. average of 75%. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Monroe County, IL R+39
- St. Louis County, MO D+28
- St. Louis City, MO D+65
- Franklin County, MO R+48
- St. Clair County, IL D+13
- Washington County, MO R+63
- St. Charles County, MO R+14
- Ste. Genevieve County, MO R+55
- St. Francois County, MO R+48
- Madison County, IL R+11
Counties with Similar Populations
- Whatcom County, WA D+23
- Richmond City, VA D+65
- Tuscaloosa County, AL R+9
- Cabarrus County, NC R+7
- Hinds County, MS D+52
- New Hanover County, NC D+5
- Gaston County, NC R+18
- Mahoning County, OH Even
- Montgomery County, AL D+38
- Barnstable County, MA D+20
All Local Stats
Home Services
Sources and methodology
Precinct-level voting records used to fit the model come from Missouri Secretary of State, 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.