78621 leans slightly Republican by roughly 10 points: about 45% of voters vote Democratic and 55% Republican.
About 56% of adults in 78621 typically vote, below the U.S. average of about 62%. Among adults in 78621, ~25% vote Democratic, ~31% Republican, and ~44% don't vote. The map below shows estimated turnout by block group.
How 78621 compares
Among zip codes within 15 miles, 78621 leans more Republican than 3 of 6 neighbors.
Politically, 78621 sits close to the rest of Texas.
Politics vary noticeably by block within 78621. The west side runs the most Democratic (D+9) and the northeast side runs the most Republican (R+39), a spread of about 48 points.
Why 78621 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 78621, not a ranked or complete list of what matters most.
Areas with many family households vote Republican. About 75% of households in 78621 are family households, about 8 points above the U.S. average of 67%.
High-school completion, uninsured rate, and voter turnout
Places that combine low high-school-completion share and a high uninsured rate tend to turn out at a lower rate, as 78621, TX does.
Why turnout in 78621 looks the way it does
Areas with limited routine healthcare access turn out at lower rates. 78621 is in the bottom quarter nationally for routine-care measures such as insurance coverage, preventive screenings, and dental visits. The uninsured rate here is about 22%, about 11 points above the U.S. average of 10%. 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 Texas Secretary of State, Elections Division, 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.