Solano County leans Democratic by roughly 20 points: about 60% of voters vote Democratic and 40% Republican.
About 56% of adults in Solano County typically vote, below the U.S. average of about 62%. Among adults in Solano County, ~34% vote Democratic, ~22% Republican, and ~44% don't vote. The map below shows estimated turnout by block group.
How Solano County compares
Among counties within 50 miles, Solano County leans more Democratic than 2 of 10 neighbors.
Politically, Solano County sits close to the rest of California.
Politics vary noticeably by city within Solano County. The southwest side runs the most Democratic (D+35) and the southeast side runs the most Republican (R+33), a spread of about 69 points.
Why Solano 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 Solano County, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 77% of residents in Solano County live in densely developed areas, about 40 points above the U.S. average of 36%. A high never-married share predicts Democratic voting, and about 35% of adults in Solano County have never been married, above 84% of counties.
Population density and Democratic lean
Places with high population density tend to lean Democratic; Solano County, CA sits in the top tenth nationally on this measure.
Why turnout in Solano County looks the way it does
Crowded housing lines up with lower turnout. About 5% of homes in Solano County have more than one occupant per room, above 94% of counties. Renters vote less often than owners, and about 36% of households in Solano County rent, above 88% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Napa County, CA D+32
- Contra Costa County, CA D+36
- Marin County, CA D+48
- Yolo County, CA D+35
- Alameda County, CA D+49
- Sonoma County, CA D+42
- San Francisco County, CA D+61
- Sacramento County, CA D+20
- San Joaquin County, CA D+4
- San Mateo County, CA D+48
Counties with Similar Populations
- York County, PA R+21
- East Baton Rouge Parish, LA D+23
- Santa Barbara County, CA D+26
- Virginia Beach City, VA D+9
- Burlington County, NJ D+16
- Hampden County, MA D+14
- Jefferson Parish, LA D+4
- Dakota County, MN D+11
- Monterey County, CA D+29
- Seminole County, FL R+5
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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.