Diamond Bar leans slightly Democratic by roughly 10 points: about 55% of voters vote Democratic and 45% Republican.
About 59% of adults in Diamond Bar typically vote, near the U.S. average of about 62%. Among adults in Diamond Bar, ~32% vote Democratic, ~27% Republican, and ~41% don't vote. The map below shows estimated turnout by block group.
How Diamond Bar compares
Among cities within 25 miles, Diamond Bar leans more Democratic than 49 of 119 neighbors.
Diamond Bar runs about 9 points more Republican than California as a whole.
Why Diamond Bar 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 Diamond Bar, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 82% of residents in Diamond Bar live in densely developed areas, about 46 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Diamond Bar sits in the top quarter (about 52%, above 94% of cities).
Population density and Democratic lean
Places with high population density tend to lean Democratic; Diamond Bar, CA sits in the top tenth nationally on this measure.
Why turnout in Diamond Bar looks the way it does
Crowded housing lines up with lower turnout. About 4% of homes in Diamond Bar have more than one occupant per room, above 84% of cities. Learn more about the findings and methodology on the political spectrum map.
Nearby Cities
- Walnut, CA D+10
- Rowland Heights, CA D+10
- South San Jose Hills, CA D+28
- Pomona, CA D+28
- Chino Hills, CA R+4
- Industry, CA D+15
- Brea, CA R+2
- West Covina, CA D+20
- San Dimas, CA D+4
- Valinda, CA D+24
Cities with Similar Populations
- Hialeah Gardens, FL R+43
- Redford, MI D+49
- Catalina Foothills, AZ D+20
- Hollister, CA D+13
- Minot, ND R+28
- Tinley Park, IL R+4
- Athens, AL R+47
- Hacienda Heights, CA D+15
- Oak Park, IL D+78
- Fuquay-Varina, NC R+4
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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.