Allegheny County leans Democratic by roughly 22 points: about 61% of voters vote Democratic and 39% Republican.
About 83% of adults in Allegheny County typically vote, above the U.S. average of about 62%. Among adults in Allegheny County, ~51% vote Democratic, ~32% Republican, and ~17% don't vote. The map below shows estimated turnout by block group.
How Allegheny County compares
Among counties within 50 miles, Allegheny County is the most Democratic-leaning.
Allegheny County runs about 24 points more Democratic than Pennsylvania as a whole. Pennsylvania is roughly evenly split, and Allegheny County sits clearly on the Democratic side.
Politics vary noticeably by city within Allegheny County. The east side is the most Democratic-leaning (D+48) and the south side is the least Democratic-leaning (D+4), a spread of about 44 points.
Why Allegheny County leans the way it does
This analysis examined 14,881 data points per county to find what predicts political lean and turnout. The items below are a few correlations that stood out for Allegheny County, not a ranked or complete list of what matters most.
Dense areas vote Democratic. About 81% of residents in Allegheny County live in densely developed areas, about 45 points above the U.S. average of 36%. High college attainment predicts Democratic voting, and Allegheny County sits in the top quarter (about 46%, above 95% of counties). A high never-married share predicts Democratic voting, and about 37% of adults in Allegheny County have never been married, above 89% of counties.
Population density and Democratic lean
Places with high population density tend to lean Democratic; Allegheny County, PA sits in the top tenth nationally on this measure.
Why turnout in Allegheny County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Allegheny County 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 66%, about 6 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 96% of adults in Allegheny County have completed high school, above 94% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Washington County, PA R+24
- Westmoreland County, PA R+26
- Beaver County, PA R+19
- Butler County, PA R+28
- Hancock County, WV R+42
- Armstrong County, PA R+52
- Brooke County, WV R+42
- Fayette County, PA R+36
- Jefferson County, OH R+35
- Greene County, PA R+43
Counties with Similar Populations
- Cuyahoga County, OH D+35
- Oakland County, MI D+14
- Hennepin County, MN D+43
- Travis County, TX D+37
- Salt Lake County, UT D+10
- Franklin County, OH D+30
- Contra Costa County, CA D+36
- Fairfax County, VA D+37
- Wake County, NC D+28
- Mecklenburg County, NC D+35
Sources and methodology
Precinct-level voting records used to fit the model come from Pennsylvania Department of State, Bureau 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.