Northumberland County leans heavily Republican by roughly 40 points: about 30% of voters vote Democratic and 70% Republican.
About 69% of adults in Northumberland County typically vote, above the U.S. average of about 62%. Among adults in Northumberland County, ~21% vote Democratic, ~48% Republican, and ~31% don't vote. The map below shows estimated turnout by block group.
How Northumberland County compares
Among counties within 50 miles, Northumberland County leans more Republican than 8 of 13 neighbors.
Northumberland County runs about 37 points more Republican than Pennsylvania as a whole.
Politics vary noticeably by city within Northumberland County. The southwest side is the most Republican-leaning (R+65) and the west side is the least Republican-leaning (R+28), a spread of about 37 points.
Why Northumberland 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 Northumberland County, not a ranked or complete list of what matters most.
Northumberland County votes Republican even though it is densely developed (about 50%, well above the Pennsylvania average of 33%). State and regional patterns outweigh the Democratic lean that density usually predicts here.
Population density and Democratic lean
Places with high population density tend to lean Democratic; Northumberland County, PA sits in the top quarter nationally on this measure.
Why turnout in Northumberland County looks the way it does
Turnout in Northumberland County sits close to the national pattern. Routine healthcare access, homeownership, education, and food security all land near their national averages here. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Montour County, PA R+23
- Union County, PA R+26
- Snyder County, PA R+50
- Columbia County, PA R+32
- Schuylkill County, PA R+36
- Lycoming County, PA R+34
- Lebanon County, PA R+31
- Juniata County, PA R+62
- Dauphin County, PA D+12
- Perry County, PA R+52
Counties with Similar Populations
- Liberty County, TX R+50
- Mendocino County, CA D+23
- Ozaukee County, WI R+7
- Frederick County, VA R+25
- Victoria County, TX R+28
- Wayne County, NY R+23
- Grafton County, NH D+18
- St. Clair County, AL R+65
- Rockingham County, NC R+31
- Madison County, KY R+26
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.