Summit leans Democratic by roughly 28 points: about 64% of voters vote Democratic and 36% Republican.
About 82% of adults in Summit typically vote, above the U.S. average of about 62%. Among adults in Summit, ~52% vote Democratic, ~29% Republican, and ~19% don't vote. The map below shows estimated turnout by block group.
How Summit compares
Among cities within 25 miles, Summit leans more Democratic than 229 of 265 neighbors.
Summit runs about 23 points more Democratic than New Jersey as a whole.
Politics vary noticeably by neighborhood within Summit. The west side is the most Democratic-leaning (D+35) and the southeast side is the least Democratic-leaning (D+24), a spread of about 11 points.
Why Summit 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 Summit, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 94% of residents in Summit live in densely developed areas, about 58 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Summit sits in the top quarter (about 75%, in the top fraction of cities).
Population density and Democratic lean
Places with high population density tend to lean Democratic; Summit, NJ sits in the top tenth nationally on this measure.
Why turnout in Summit looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Summit 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 76%, about 16 points above the U.S. average of 60%. Learn more about the findings and methodology on the political spectrum map.
Nearby Cities
- Chatham, NJ D+18
- New Providence, NJ D+19
- Springfield, NJ D+18
- Short Hills, NJ D+35
- Mountainside, NJ Even
- Millburn, NJ D+46
- Madison, NJ D+22
- Green Village, NJ D+5
- Vauxhall, NJ D+74
- Florham Park, NJ D+6
Cities with Similar Populations
- Central Falls, RI D+23
- Montclair, VA D+27
- Red Lion, PA R+28
- Evans, CO R+12
- Union Hill-Novelty Hill, WA D+33
- Oroville, CA R+21
- Fountain Inn, SC R+30
- Acton, MA D+43
- Seaford, DE R+10
- Gretna, LA D+20
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Sources and methodology
Precinct-level voting records used to fit the model come from New Jersey Division of 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.