St. Louis County leans Democratic by roughly 28 points: about 64% of voters vote Democratic and 36% Republican.
About 73% of adults in St. Louis County typically vote, above the U.S. average of about 62%. Among adults in St. Louis County, ~47% vote Democratic, ~26% Republican, and ~27% don't vote. The map below shows estimated turnout by block group.
How St. Louis County compares
Among counties within 50 miles, St. Louis County leans more Democratic than 12 of 13 neighbors.
St. Louis County runs about 46 points more Democratic than Missouri as a whole. Missouri leans Republican overall, while St. Louis County is one of the few Democratic-leaning pockets.
Politics vary noticeably by city within St. Louis County. The east side runs the most Democratic (D+73) and the southwest side runs the most Republican (Even), a spread of about 74 points.
Why St. Louis 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 St. Louis County, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 92% of residents in St. Louis County live in densely developed areas, about 55 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and St. Louis County sits in the top quarter (about 47%, above 96% of counties). St. Louis County runs against the grain of Missouri, a Democratic-leaning pocket in a Republican-leaning state.
Walkability and Democratic lean
Places with a highly walkable street grid tend to lean Democratic; St. Louis County, MO 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 St. Louis County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. St. Louis 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%, above 77% of counties. High high-school completion lines up with higher turnout, and about 94% of adults in St. Louis County have completed high school, above 88% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- St. Louis City, MO D+65
- St. Charles County, MO R+14
- Jefferson County, MO R+39
- St. Clair County, IL D+13
- Monroe County, IL R+39
- Madison County, IL R+11
- Jersey County, IL R+44
- Calhoun County, IL R+56
- Franklin County, MO R+48
- Lincoln County, MO R+51
Counties with Similar Populations
- Westchester County, NY D+27
- Fresno County, CA D+3
- Duval County, FL D+7
- Honolulu County, HI D+18
- Marion County, IN D+29
- Prince George's County, MD D+71
- Pima County, AZ D+16
- Pinellas County, FL R+3
- Gwinnett County, GA D+21
- Bergen County, NJ D+5
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.