Sully County is a Republican stronghold. About 19% of voters here vote Democratic and 81% Republican.
About 69% of adults in Sully County typically vote, above the U.S. average of about 62%. Among adults in Sully County, ~13% vote Democratic, ~56% Republican, and ~31% don't vote. The map below shows estimated turnout by block group.
How Sully County compares
Among counties within 50 miles, Sully County leans more Republican than 3 of 4 neighbors.
Sully County runs about 33 points more Republican than South Dakota as a whole.
Why Sully County leans the way it does
Density, race composition, education, and family structure all sit close to their national averages in Sully County. The lean here lands roughly where demographic data alone would predict.
Park access and Republican lean
Places with low park coverage tend to lean Republican; Sully County, SD sits in the bottom tenth nationally on this measure. Park access does not change how people vote; it tends to track denser, higher-income areas.
Why turnout in Sully County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Sully 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 72%, about 12 points above the U.S. average of 60%. High high-school completion lines up with higher turnout, and about 96% of adults in Sully County have completed high school, above 97% of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Hughes County, SD R+34
- Potter County, SD R+62
- Stanley County, SD R+49
- Hyde County, SD R+60
- Dewey County, SD D+30
- Lyman County, SD R+5
- Faulk County, SD R+66
- Walworth County, SD R+56
- Hand County, SD R+62
- Buffalo County, SD D+24
Counties with Similar Populations
- Kiowa County, CO R+72
- Wheeler County, OR R+51
- Throckmorton County, TX R+76
- Piute County, UT R+78
- Briscoe County, TX R+71
- Edwards County, TX R+42
- Lake and Peninsula Borough, AK D+13
- Carter County, MT R+78
- Wallace County, KS R+83
- Cottle County, TX R+57
Sources and methodology
Precinct-level voting records used to fit the model come from South Dakota Secretary of State, 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.