Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Petroleum County, Montana
EPA puts Petroleum County in Zone 2, its middle radon zone. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
72.2%
Fergus County
- Fergus
- 72.2%
1 of 5 neighbours have 30+ tests, 2006 to 2015
Nearest county
72.2%
Fergus County, 47 miles
- Fergus
- 72.2%
- Montana
- 47.4%
Share at 4+ pCi/L, 72 tests, 2006 to 2015
Ground above low
100.0%
Level with Montana
- Petroleum
- 100.0%
- Montana
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
0
None published
A home here needs its own test
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Petroleum County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
The data
Petroleum County, At a glance
Petroleum County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Petroleum County is a
USGS geologic potential: Moderate across 87% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
No CDC test figures here
CDC has published no radon test figures for Petroleum County. Fergus County, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 72.2% of its tests at or above 4 pCi/L.
Petroleum County, Compared
Petroleum County radon figures, compared
Calculated by Radon411Petroleum County has no radon test figure of its own from CDC, whose counts over the 2006 to 2015 laboratory totals name 52 other Montana counties and leave it out. Pooled across 52 Montana counties, 47.4% of reported tests reached that level; across every county in the country with a figure, 36.3%.
Fergus County, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 72.2% of its tests at or above 4 pCi/L. Farther out, Yellowstone County (82 miles away) at 43.1%, Judith Basin County (95 miles away) at 64.3% and Valley County (113 miles away) at 50.0% have figures too. Statewide for the same period, Sheridan County reported the highest share (75.7%) and Hill County the lowest (35.0%).
EPA's 1993 map puts Petroleum County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 87% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Petroleum County, Geology
The ground under Petroleum County
PredictedMost of the ground under Petroleum County is one class on USGS's geologic map: 86.6% of its land is moderate radon potential, with 13.4% high. The map puts 86.6% of Petroleum County in the area it calls Plains and Mountains and 13.4% in Great Plains (Glaciated). USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Plains and Mountains | Marine and continental shale, siltstone, and sandstone of Cretaceous and Tertiary ages, and volcanic rocks. | Moderate | 10 | 86.6% |
| Great Plains (Glaciated) | Glacial deposits derived from Cretaceous shales containing higher than average amounts of uranium. | High | 13 | 13.4% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Petroleum County beside the ground around it
Montana as a whole has more high-potential ground than Petroleum County: 78.5% of its land, against 13.4% here. Of the 5 counties that border it, 4 have more high-potential ground, Phillips County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Petroleum County, Local resources
Radon testing and mitigation in Petroleum County
- Radon Control ProgramRadon Control Program, run by Montana DEQ, does not license radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Montana.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Energy Bureau staff manage the radon information toll-free hotline and distribute subsidized radon test kits to Montana residents.
- Compare kits
- See the Montana directoryNo professionals are listed in Montana yet. The state program can point you to registered testers and mitigators.
What Montana's program says
- Phone
- 1-800-546-0483
- Licensing of radon professionals
Montana DEQ does not certify or require proof of certification for the contractors listed.
What it means
Petroleum County, Questions
Questions about radon in Petroleum County
Are radon levels high in Petroleum County?
No CDC testing statistics are published here for Petroleum County, Montana yet. Fergus County, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 72.2% of its tests at or above 4 pCi/L.
Which counties border Petroleum County?
Petroleum County borders 5 counties: Fergus County, Musselshell County, Garfield County, Phillips County and Rosebud County.
Products
Petroleum County, Products
Testing a home in Petroleum County
No CDC figure names Petroleum County; the nearest county with one, Fergus County (47 miles away), reported 72.2% of its tests at or above 4 pCi/L over the 2006 to 2015 laboratory totals, the only reading nearby until a test of this home. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Petroleum County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Monitor
Wave Radon battery smart radon monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- App only
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Petroleum County, Bordering counties
Counties bordering Petroleum County
Calculated by Radon411- Radon levels in Phillips CountyEPA zone 1
100.0%at or above 4 pCi/L
Median 6.2 pCi/L · 2 tests
- Radon levels in Fergus CountyEPA zone 1
72.2%at or above 4 pCi/L
Median 7.0 pCi/L · 72 tests
- Radon levels in Rosebud CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 4.4 pCi/L · 6 tests
- Radon levels in Musselshell CountyEPA zone 2
28.6%at or above 4 pCi/L
Median 2.7 pCi/L · 14 tests
- Radon levels in Garfield CountyEPA zone 1
No CDC figure for 2006 to 2015; its page reads it against its own neighbours.
Petroleum County, Cities and towns
Cities and towns in Petroleum County
Petroleum County is growing: the Census Bureau puts it at 548 residents on July 1, 2025, up 9.2% from 502 in 2020. Spread over its land, that is 0.3 people to the square mile. Winnett, its one incorporated place, has 205 residents, 37.4% of the total. CDC publishes no radon test count for Petroleum County; across Montana its counts for 2006 to 2015 come to 7.5 tests for every 1,000 residents (2025 estimate).
Winnett is the one incorporated place here; CDC publishes no figure by town, so it reads Petroleum County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Winnett | 205 | +9.6% | 37.4% |
One incorporated place, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Petroleum County, Homes
Homes in Petroleum County
Petroleum County is a place of houses on their own lots: 77% of its 295 homes are detached single-family houses, against 69% across Montana. Half of its homes were built before 1978, close to Montana's 1980: 34% date from before 1960 and 12% from 2000 or later. Owners live in 77% of the occupied homes (Montana: 69%), so for most households a test and a fix are their own to order.
| Homes | Petroleum County | Montana |
|---|---|---|
| Housing units | 295 | 522,939 |
| Detached houses | 77% | 69% |
| In buildings of 5 or more | 0% | 9% |
| Mobile homes | 22% | 10% |
| Built before 1960 | 34% | 26% |
| Built since 2000 | 12% | 27% |
| Middle year built | 1978 | 1980 |
| Owner-occupied | 77% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.