Petroleum County is a Republican stronghold. About 16% of voters here vote Democratic and 84% Republican.
About 81% of adults in Petroleum County typically vote, above the U.S. average of about 62%. Among adults in Petroleum County, ~13% vote Democratic, ~68% Republican, and ~19% don't vote. The map below shows estimated turnout by block group.
How Petroleum County compares
Petroleum County runs about 49 points more Republican than Montana as a whole.
Why Petroleum 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 Petroleum County, not a ranked or complete list of what matters most.
Rural areas with a high white share vote Republican. Petroleum County sits in the bottom quarter on density and about 99% of residents are non-Hispanic white, about 16 points above the Montana average of 83%.
Paved land cover and Republican lean
Places with little paved surface tend to lean Republican; Petroleum County, MT 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 Petroleum County looks the way it does
Areas with strong routine healthcare access turn out at higher rates. Petroleum 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 63%, above 69% of counties. High high-school completion lines up with higher turnout, and about 99% of adults in Petroleum County have completed high school, in the top fraction of counties. Learn more about the findings and methodology on the political spectrum map.
Nearby Counties
- Musselshell County, MT R+64
- Fergus County, MT R+50
- Golden Valley County, MT R+69
- Garfield County, MT R+87
- Treasure County, MT R+66
- Wheatland County, MT R+66
- Yellowstone County, MT R+25
- Judith Basin County, MT R+62
- Phillips County, MT R+52
- Blaine County, MT Even
Counties with Similar Populations
- Arthur County, NE R+59
- Blaine County, NE R+81
- McPherson County, NE R+84
- McMullen County, TX R+59
- Loup County, NE R+72
- Grant County, NE R+84
- Borden County, TX R+93
- Kenedy County, TX R+44
- Harding County, NM R+37
- Yakutat City and Borough, AK Even
Sources and methodology
Precinct-level voting records used to fit the model come from Montana 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.