Boulder County is a Democratic stronghold. About 76% of voters here vote Democratic and 24% Republican.
About 82% of adults in Boulder County typically vote, above the U.S. average of about 62%. Among adults in Boulder County, ~62% vote Democratic, ~20% Republican, and ~18% don't vote. The map below shows estimated turnout by block group.
How Boulder County compares
Among counties within 50 miles, Boulder County leans more Democratic than 10 of 11 neighbors.
Boulder County runs about 42 points more Democratic than Colorado as a whole.
Politics vary noticeably by city within Boulder County. The west side is the most Democratic-leaning (D+71) and the northeast side is the least Democratic-leaning (D+33), a spread of about 37 points.
Why Boulder 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 Boulder County, not a ranked or complete list of what matters most.
Areas with high college attainment vote Democratic. About 65% of adults in Boulder County hold a bachelor's degree, about 36 points above the U.S. average of 28%. Dense areas vote Democratic, and Boulder County sits in the top fifth on density (about 79%, above 95% of counties). A high never-married share predicts Democratic voting, and about 38% of adults in Boulder County have never been married, above 91% of counties.
Population density and Democratic lean
Places with high population density tend to lean Democratic; Boulder County, CO sits in the top tenth nationally on this measure.
Why turnout in Boulder County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Boulder 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 70%, about 10 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 96% of adults in Boulder County have completed high school, above 96% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Broomfield County, CO D+25
- Adams County, CO D+11
- Gilpin County, CO D+16
- Jefferson County, CO D+18
- Denver County, CO D+53
- Weld County, CO R+17
- Clear Creek County, CO D+21
- Larimer County, CO D+16
- Arapahoe County, CO D+22
- Grand County, CO R+6
Counties with Similar Populations
- St. Lucie County, FL R+5
- Howard County, MD D+40
- Weld County, CO R+17
- Spartanburg County, SC R+25
- Henrico County, VA D+31
- Cumberland County, NC D+20
- Luzerne County, PA R+14
- Durham County, NC D+59
- Rockland County, NY R+14
- Lancaster County, NE D+7
All Local Stats
Home Services
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.