Castro Valley leans heavily Democratic by roughly 34 points: about 67% of voters vote Democratic and 33% Republican.
About 60% of adults in Castro Valley typically vote, near the U.S. average of about 62%. Among adults in Castro Valley, ~40% vote Democratic, ~20% Republican, and ~40% don't vote. The map below shows estimated turnout by block group.
How Castro Valley compares
Among cities within 25 miles, Castro Valley leans more Democratic than 13 of 81 neighbors.
Castro Valley runs about 13 points more Democratic than California as a whole.
Politics vary noticeably by neighborhood within Castro Valley. The southwest side is the most Democratic-leaning (D+44) and the northeast side is the least Democratic-leaning (D+17), a spread of about 27 points.
Why Castro Valley leans the way it does
This analysis examined 14,881 data points per city to find what predicts political lean and turnout. The items below are a few correlations that stood out for Castro Valley, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 83% of residents in Castro Valley live in densely developed areas, about 47 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Castro Valley sits in the top quarter (about 45%, above 91% of cities).
Walkability and Democratic lean
Places with a highly walkable street grid tend to lean Democratic; Castro Valley, 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 Castro Valley looks the way it does
Crowded housing lines up with lower turnout. About 6% of homes in Castro Valley have more than one occupant per room, above 90% of cities. Strong routine healthcare access lines up with higher turnout, and Castro Valley sits in the top quarter on routine-care measures. Learn more about the findings and methodology on the political spectrum map.
Nearby Cities
- Fairview, CA D+42
- Ashland, CA D+45
- Cherryland, CA D+39
- San Lorenzo, CA D+34
- Hayward, CA D+38
- San Leandro, CA D+41
- Union City, CA D+33
- San Ramon, CA D+34
- Dublin, CA D+35
- Danville, CA D+27
Cities with Similar Populations
- Waltham, MA D+43
- San Luis Obispo, CA D+39
- Lorain, OH D+14
- Casa Grande, AZ R+14
- Hanford, CA R+15
- Arcadia, CA D+14
- Joplin, MO R+33
- North Richland Hills, TX R+21
- Wilkes-Barre, PA D+4
- Northglenn, CO D+12
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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.