57640 is a Republican stronghold. About 15% of voters here vote Democratic and 85% Republican.
About 76% of adults in 57640 typically vote, above the U.S. average of about 62%. Among adults in 57640, ~11% vote Democratic, ~64% Republican, and ~25% don't vote. The map below shows estimated turnout by block group.
How 57640 compares
57640 runs about 40 points more Republican than South Dakota as a whole.
Why 57640 leans the way it does
This analysis examined 14,881 data points per zip code to find what predicts political lean and turnout. The items below are a few correlations that stood out for 57640, not a ranked or complete list of what matters most.
Rural areas with a high white share vote Republican. 57640 sits in the bottom quarter on density and about 95% of residents are non-Hispanic white, about 14 points above the South Dakota average of 81%. A high family-household share predicts Republican voting, and about 80% of households in 57640 are family households, above 92% of zip codes.
Paved land cover and Republican lean
Places with little paved surface tend to lean Republican; 57640, SD sits in the bottom tenth nationally on this measure. Paved ground does not change how people vote; it mostly reflects how urban and built-up a place is.
Why turnout in 57640 looks the way it does
Areas with high high-school completion turn out at higher rates. About 97% of adults in 57640 have completed high school, about 7 points above the U.S. average of 90%. Learn more about the findings and methodology on the political spectrum map.
Nearby Zip Codes
Zip Codes with Similar Populations
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.