Mountainside is a true toss-up. About 50% of voters here vote Democratic and 50% Republican.
About 94% of adults in Mountainside typically vote, above the U.S. average of about 62%. Among adults in Mountainside, ~47% vote Democratic, ~47% Republican, and ~6% don't vote. The map below shows estimated turnout by block group.
How Mountainside compares
Among cities within 25 miles, Mountainside sits roughly in the middle of the political spectrum, with 150 neighbors leaning further in the place's direction and 111 leaning the other way.
Mountainside runs about 7 points more Republican than New Jersey as a whole.
Politics vary noticeably by neighborhood within Mountainside. The southwest side runs the most Democratic (D+6) and the northwest side runs the most Republican (R+6), a spread of about 12 points.
Why Mountainside leans the way it does
Density, race composition, education, and family structure all sit close to their national averages in Mountainside. The lean here lands roughly where demographic data alone would predict.
Cancer-screening access and voter turnout
Places with high colon-cancer-screening access tend to turn out at a higher rate; Mountainside, NJ sits in the top quarter nationally on this measure. Cancer screening does not drive turnout; it reflects income, insurance, and healthcare access.
Why turnout in Mountainside looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Mountainside 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 77%, about 17 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 97% of adults in Mountainside have completed high school, above 92% of cities. Learn more about the findings and methodology on the political spectrum map.
Nearby Cities
- Westfield, NJ D+27
- Springfield, NJ D+18
- Garwood, NJ Even
- Summit, NJ D+29
- New Providence, NJ D+19
- Fanwood, NJ D+29
- Scotch Plains, NJ D+23
- Cranford, NJ D+16
- Kenilworth, NJ R+22
- Berkeley Heights, NJ D+11
Cities with Similar Populations
- Baldwin Harbor, NY D+39
- Castroville, TX R+33
- Wadesboro, NC D+22
- Trinity, TX R+53
- Monticello, FL R+17
- Sunnyvale, TX R+19
- Dormont, PA D+39
- Tomahawk, WI R+28
- Louisburg, KS R+39
- Rocky Face, GA R+65
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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.