Sonoma County, CA Political Map | Democrat & Republican Areas in Sonoma County

By the BestNeighborhood data science team. Last updated May 2026.

Sonoma County leans heavily Democratic by roughly 42 points: about 71% of voters vote Democratic and 29% Republican.

 

About 66% of adults in Sonoma County typically vote, near the U.S. average of about 62%. Among adults in Sonoma County, ~47% vote Democratic, ~19% Republican, and ~34% don't vote. The map below shows estimated turnout by block group.

How Sonoma County compares

Among counties within 50 miles, Sonoma County leans more Democratic than 3 of 5 neighbors.

Sonoma County runs about 22 points more Democratic than California as a whole.

Politics vary noticeably by city within Sonoma County. The west side is the most Democratic-leaning (D+51) and the north side is the least Democratic-leaning (D+34), a spread of about 17 points.

Why Sonoma 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 Sonoma County, not a ranked or complete list of what matters most.

Dense areas vote Democratic. About 74% of residents in Sonoma County live in densely developed areas, about 38 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Sonoma County sits in the top quarter (about 38%, above 89% of counties). A high never-married share predicts Democratic voting, and about 33% of adults in Sonoma County have never been married, above 78% of counties.

Walkability and Democratic lean

Places with a highly walkable street grid tend to lean Democratic; Sonoma County, CA 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 Sonoma County looks the way it does

Areas with strong routine healthcare access turn out at higher rates. Sonoma 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 67%, about 7 points above the U.S. average of 60%. Learn more about the findings and methodology on the political spectrum map.

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Sources and methodology

Precinct-level voting records used to fit the model come from California 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.