Jefferson County leans Democratic by roughly 18 points: about 59% of voters vote Democratic and 41% Republican.
About 84% of adults in Jefferson County typically vote, above the U.S. average of about 62%. Among adults in Jefferson County, ~50% vote Democratic, ~34% Republican, and ~16% 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 Democratic than 6 of 11 neighbors.
Jefferson County runs about 7 points more Democratic than Colorado as a whole.
Politics vary noticeably by city within Jefferson County. The east side is the most Democratic-leaning (D+32) and the northwest side is the least Democratic-leaning (D+8), 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.
Dense areas vote Democratic. About 83% of residents in Jefferson County live in densely developed areas, about 47 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Jefferson County sits in the top quarter (about 52%, above 98% of counties).
Population density and Democratic lean
Places with high population density tend to lean Democratic; Jefferson County, CO sits in the top tenth nationally on this measure.
Why turnout in Jefferson County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Jefferson 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 69%, about 9 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 96% of adults in Jefferson County have completed high school, above 96% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Denver County, CO D+53
- Adams County, CO D+11
- Broomfield County, CO D+25
- Arapahoe County, CO D+22
- Gilpin County, CO D+16
- Clear Creek County, CO D+21
- Douglas County, CO R+7
- Boulder County, CO D+52
- Park County, CO R+9
- Elbert County, CO R+46
Counties with Similar Populations
- Douglas County, NE D+17
- Baltimore City, MD D+72
- Bristol County, MA Even
- Anne Arundel County, MD D+17
- Delaware County, PA D+27
- Union County, NJ D+26
- New Castle County, DE D+33
- Washington County, OR D+32
- Pasco County, FL R+24
- Dane County, WI D+48
Sources and methodology
Precinct-level voting records used to fit the model come from Colorado 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.