Seneca leans heavily Republican by roughly 30 points: about 35% of voters vote Democratic and 65% Republican.
About 88% of adults in Seneca typically vote, above the U.S. average of about 62%. Among adults in Seneca, ~31% vote Democratic, ~57% Republican, and ~12% don't vote. The map below shows estimated turnout by block group.
How Seneca compares
Among cities within 25 miles, Seneca leans more Republican than 19 of 67 neighbors.
Seneca runs about 42 points more Republican than Illinois as a whole. Illinois leans Democratic overall, while Seneca is one of the few Republican-leaning pockets.
Politics vary noticeably by neighborhood within Seneca. The southeast side is the most Republican-leaning (R+41) and the west side is the least Republican-leaning (R+26), a spread of about 15 points.
Why Seneca 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 Seneca, not a ranked or complete list of what matters most.
Seneca votes against the grain of Illinois. Illinois leans Democratic overall, while Seneca runs about 42 points more Republican. Dense places usually vote Democratic, but Seneca runs against that pattern.
Walkability and Democratic lean
Places with a highly walkable street grid tend to lean Democratic; Seneca, IL sits in the top quarter nationally on this measure. A walkable street grid does not change how people vote; it mostly reflects how urban a place is.
Why turnout in Seneca looks the way it does
Turnout in Seneca 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 Cities
- Marseilles, IL R+26
- Stavanger, IL R+39
- Verona, IL R+48
- Kinsman, IL R+49
- Ransom, IL R+42
- Morris, IL R+23
- Mazon, IL R+42
- Woodland Addition, IL R+34
- Lisbon, IL R+46
Cities with Similar Populations
- Limon, CO R+58
- West Farmington, OH R+55
- Soda Springs, ID R+72
- Harbour Heights, FL R+34
- Greenwich, OH R+61
- Bainbridge, NY R+39
- Pistakee Highlands, IL R+14
- Yucca, AZ R+37
- Ochlocknee, GA R+69
- Tybee Island, GA R+28
All Local Stats
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Sources and methodology
Precinct-level voting records used to fit the model come from Illinois State Board 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.