Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Big Horn County, Montana
EPA puts Big Horn County in Zone 1, its highest radon zone, and only 21 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
70.3%
Sheridan County
- Sheridan
- 70.3%
- Yellowstone
- 43.1%
4 of 7 neighbours have 30+ tests, 2006 to 2015
Nearest county
43.1%
Yellowstone County, 52 miles
- Yellowstone
- 43.1%
- Montana
- 47.4%
Share at 4+ pCi/L, 1,421 tests, 2006 to 2015
Ground above low
100.0%
Level with Montana
- Big Horn
- 100.0%
- Montana
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
22
Too few for a share
- Big Horn
- 22
- Needed
- 30
2007 to 2016, laboratory
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Read a result for Big Horn 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
Big Horn County, At a glance
Big Horn County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Big Horn County in
USGS geologic potential: High across 50% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Big Horn County, 2008 to 2017, laboratory
CDC holds 21 reported tests for Big Horn County over the 2008 to 2017 laboratory totals, with a median of 2.0 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Big Horn County beside the counties around it is how this page reads it.
What these figures count
Only 21 tests were reported to CDC for Big Horn County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Big Horn County, Compared
Big Horn County radon figures, compared
Calculated by Radon411CDC's largest figure for Big Horn County rests on 22 tests over the 2007 to 2016 laboratory totals, 6 of them at or above 4 pCi/L, so each test moves its share by 4.5 points and no rank or comparison is drawn from it. Results reached as high as 11.0 pCi/L, with a middle value of 1.9 pCi/L.
Of the counties bordering it, 4 have a figure over the 2006 to 2015 laboratory totals: Sheridan County, WY reported the largest share at or above 4 pCi/L, 70.3%, and Yellowstone County the smallest, 43.1%, with Carbon County at 52.5% and Big Horn County, WY at 44.2% between. Farther out, Stillwater County (94 miles away) at 61.8%, Park County (148 miles away) at 57.9% and Fergus County (152 miles away) at 72.2% have figures too. Pooled across 52 Montana counties, 47.4% of reported tests reached that level; across every county in the country with a figure, 36.3%.
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 Big Horn County in Zone 1, the map's highest label: a predicted county average above 4 pCi/L. USGS geology rates 50% of the county's land high radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Big Horn County, Geology
The ground under Big Horn County
PredictedUSGS's geologic map splits Big Horn County: 50.2% of its land is high radon potential and 49.8% moderate. The map puts 49.8% of Big Horn County in the area it calls Plains and Mountains and 32.5% in Great Plains, with one smaller area beside them. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 12, 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 | 49.8% |
| Great Plains | Tertiary sandstone, siltstone, shale, coal. | High | 12 | 32.5% |
| Big Horn Mountains | Granitic and metamorphic rocks. | High | 13 | 17.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Big Horn County beside the ground around it
Montana as a whole has more high-potential ground than Big Horn County: 78.5% of its land, against 50.2% here. Of the 7 counties that border it, 4 have more high-potential ground, Big Horn County, WY the most at 100%.
The map rates the ground, not the air in any home.
Local help
Big Horn County, Local resources
Radon testing and mitigation in Big Horn 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
Big Horn County, Questions
Questions about radon in Big Horn County
Are radon levels high in Big Horn County?
Over the 2008 to 2017 laboratory totals, 28.6% of the radon tests reported to CDC for Big Horn County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.0 pCi/L. Of the counties bordering it, 4 have a figure over the 2006 to 2015 laboratory totals: Sheridan County, WY reported the largest share at or above 4 pCi/L, 70.3%, and Yellowstone County the smallest, 43.1%, with Carbon County at 52.5% and Big Horn County, WY at 44.2% between.
Which counties border Big Horn County?
Big Horn County borders 7 counties: Treasure County, MT, Rosebud County, MT, Yellowstone County, MT, Sheridan County, WY, Big Horn County, WY, Powder River County, MT and Carbon County, MT.
Products
Big Horn County, Products
Testing a home in Big Horn County
No CDC figure names Big Horn County; the nearest county with one, Yellowstone County (52 miles away), reported 43.1% 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 1 the year-round level in Big Horn County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorForensics Detectors
FD-65-RADON rechargeable radon detector with a color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Big Horn County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Big Horn County
Explore
Big Horn County, Bordering counties
Counties bordering Big Horn County
Calculated by Radon411- Radon levels in Powder River County, MTEPA zone 1
71.4%at or above 4 pCi/L
Median 4.5 pCi/L · 7 tests
- Radon levels in Sheridan County, WYEPA zone 1
70.3%at or above 4 pCi/L
Median 5.9 pCi/L · 852 tests
- Radon levels in Carbon County, MTEPA zone 1
52.5%at or above 4 pCi/L
Median 4.0 pCi/L · 40 tests
- Radon levels in Rosebud County, MTEPA zone 1
50.0%at or above 4 pCi/L
Median 4.4 pCi/L · 6 tests
- Radon levels in Big Horn County, WYEPA zone 1
44.2%at or above 4 pCi/L
Median 3.5 pCi/L · 86 tests
- Radon levels in Yellowstone County, MTEPA zone 2
43.1%at or above 4 pCi/L
Median 3.5 pCi/L · 1,421 tests
- Radon levels in Treasure County, MTEPA zone 2
No CDC figure for 2006 to 2015; its page reads it against its own neighbours.
Big Horn County, Cities and towns
Cities and towns in Big Horn County
About 12,752 people live in Big Horn County by the Census Bureau's estimate for July 1, 2025, 327 fewer than in 2020 (−2.5%). Spread over its land, that is 2.6 people to the square mile. Its largest town, Hardin, has 3,696 residents, 29.0% of the total. Together its 2 incorporated places hold 32.3% of those residents; the other 67.7% live outside any of them. Reported testing is thin here: 22 tests over 2007 to 2016, or 1.7 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.1.
From Hardin to Lodge Grass, CDC publishes no figure by town: each reads Big Horn County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Hardin | 3,696 | −2.6% | 29.0% |
| Lodge Grass | 422 | −3.4% | 3.3% |
2 incorporated places, 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).
Big Horn County, Homes
Homes in Big Horn County
Of Big Horn County's 4,533 homes, 69% are detached houses, against 69% across Montana; 18% are mobile homes. Half of its homes were built before 1976, close to Montana's 1980: 25% date from before 1960 and 14% from 2000 or later. 68% of occupied homes are lived in by their owner (Montana: 69%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Big Horn County | Montana |
|---|---|---|
| Housing units | 4,533 | 522,939 |
| Detached houses | 69% | 69% |
| In buildings of 5 or more | 6% | 9% |
| Mobile homes | 18% | 10% |
| Built before 1960 | 25% | 26% |
| Built since 2000 | 14% | 27% |
| Middle year built | 1976 | 1980 |
| Owner-occupied | 68% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.