91791 leans Democratic by roughly 16 points: about 58% of voters vote Democratic and 42% Republican.
About 61% of adults in 91791 typically vote, near the U.S. average of about 62%. Among adults in 91791, ~35% vote Democratic, ~26% Republican, and ~39% don't vote. The map below shows estimated turnout by block group.
How 91791 compares
Among zip codes within 15 miles, 91791 leans more Democratic than 32 of 72 neighbors.
Politically, 91791 sits close to the rest of California.
Politics vary noticeably by block within 91791. The north side is the most Democratic-leaning (D+24) and the southeast side is the least Democratic-leaning (D+7), a spread of about 17 points.
Why 91791 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 91791, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 96% of residents in 91791 live in densely developed areas, about 60 points above the U.S. average of 36%. A high never-married share predicts Democratic voting, and about 35% of adults in 91791 have never been married, above 79% of zip codes.
Population density and Democratic lean
Places with high population density tend to lean Democratic; 91791, CA sits in the top tenth nationally on this measure.
Why turnout in 91791 looks the way it does
Crowded housing lines up with lower turnout. About 7% of homes in 91791 have more than one occupant per room, above 92% of zip codes. Low high-school completion lines up with lower turnout, and about 87% of adults in 91791 have completed high school, below 75% of zip codes. 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.