91321 leans slightly Democratic by roughly 8 points: about 54% of voters vote Democratic and 46% Republican.
About 56% of adults in 91321 typically vote, below the U.S. average of about 62%. Among adults in 91321, ~30% vote Democratic, ~26% Republican, and ~44% don't vote. The map below shows estimated turnout by block group.
How 91321 compares
Among zip codes within 15 miles, 91321 leans more Democratic than 9 of 37 neighbors.
91321 runs about 12 points more Republican than California as a whole.
Politics vary noticeably by block within 91321. The northwest side runs the most Democratic (D+21) and the north side runs the most Republican (R+11), a spread of about 32 points.
Why 91321 leans the way it does
This analysis examined 14,881 data points per zip code to find what predicts political lean and turnout. The items below are a few correlations that stood out for 91321, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 85% of residents in 91321 live in densely developed areas, about 49 points above the U.S. average of 36%. A high never-married share predicts Democratic voting, and about 37% of adults in 91321 have never been married, above 83% of zip codes.
Paved land cover and Democratic lean
Places with extensive paved surfaces tend to lean Democratic; 91321, CA sits in the top quarter nationally on this measure. Paved ground does not change how people vote; it mostly reflects how urban and built-up a place is.
Why turnout in 91321 looks the way it does
Crowded housing lines up with lower turnout. About 10% of homes in 91321 have more than one occupant per room, above 96% of zip codes. Renters vote less often than owners, and about 41% of households in 91321 rent, about 16 points above the U.S. average of 25%. Learn more about the findings and methodology on the political spectrum map.
Nearby Zip Codes
Zip Codes with Similar Populations
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.