Mercer County leans heavily Republican by roughly 34 points: about 33% of voters vote Democratic and 67% Republican.
About 83% of adults in Mercer County typically vote, above the U.S. average of about 62%. Among adults in Mercer County, ~27% vote Democratic, ~56% Republican, and ~17% don't vote. The map below shows estimated turnout by block group.
How Mercer County compares
Among counties within 50 miles, Mercer County leans more Republican than 9 of 13 neighbors.
Mercer County runs about 44 points more Republican than Illinois as a whole. Illinois leans Democratic overall, while Mercer County is one of the few Republican-leaning pockets.
Politics vary noticeably by city within Mercer County. The northwest side is the most Republican-leaning (R+51) and the east side is the least Republican-leaning (R+28), a spread of about 22 points.
Why Mercer 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 Mercer County, not a ranked or complete list of what matters most.
Mercer County votes against the grain of Illinois. Illinois leans Democratic overall, while Mercer County runs about 44 points more Republican. Rural areas with a high white share vote Republican. Non-Hispanic white share in Mercer County is about 93%, well above similar-sized counties (around 76%).
Population density and Republican lean
Places with low population density tend to lean Republican; Mercer County, IL sits below the national average on this measure.
Why turnout in Mercer County looks the way it does
Homeowners vote more often than renters. About 84% of households in Mercer County own their home, about 9 points above the U.S. average of 75%. High high-school completion lines up with higher turnout, and about 94% of adults in Mercer County have completed high school, above 81% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Rock Island County, IL D+12
- Warren County, IL R+22
- Scott County, IA D+5
- Muscatine County, IA R+16
- Knox County, IL R+9
- Louisa County, IA R+37
- Henry County, IL R+24
- Henderson County, IL R+41
- Des Moines County, IA R+8
- Cedar County, IA R+34
Counties with Similar Populations
- Aitkin County, MN R+33
- Carroll County, IL R+34
- Jefferson County, GA D+5
- Grand County, CO R+6
- Leon County, TX R+69
- Henry County, KY R+51
- Jefferson County, IA R+4
- Pemiscot County, MO R+30
- Nottoway County, VA R+9
- Osage County, KS R+49
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.