91423 leans heavily Democratic by roughly 44 points: about 72% of voters vote Democratic and 28% Republican.
About 67% of adults in 91423 typically vote, near the U.S. average of about 62%. Among adults in 91423, ~48% vote Democratic, ~19% Republican, and ~33% don't vote. The map below shows estimated turnout by block group.
How 91423 compares
Among zip codes within 15 miles, 91423 leans more Democratic than 65 of 129 neighbors.
91423 runs about 23 points more Democratic than California as a whole.
Politics vary noticeably by block within 91423. The northeast side is the most Democratic-leaning (D+48) and the southwest side is the least Democratic-leaning (D+37), a spread of about 11 points.
Why 91423 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 91423, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 98% of residents in 91423 live in densely developed areas, about 62 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and 91423 sits in the top quarter (about 64%, above 96% of zip codes). A high never-married share predicts Democratic voting, and about 44% of adults in 91423 have never been married, above 91% of zip codes.
Population density and Democratic lean
Places with high population density tend to lean Democratic; 91423, CA sits in the top tenth nationally on this measure.
Why turnout in 91423 looks the way it does
Areas with strong routine healthcare access turn out at higher rates. 91423 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 72%, about 12 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 96% of adults in 91423 have completed high school, above 85% 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.