Skip to content
RADON411

Locations and reports

Radon Levels in Carbon County, Montana

EPA puts Carbon County in Zone 1, its highest radon zone, and high results are common there: 52.2% of the 46 radon tests reported to CDC (2008 to 2017, laboratory totals) came back at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    52.2%

    6.7 pts above MT

    Carbon
    52.2%
    Montana
    45.5%

    46 tests, 2008 to 2017

  • Median result

    4.2pCi/L

    Action level reached

    Carbon
    4.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    46

    18th of 23 by tests

    Carbon
    46
    Missoula
    2,613

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Montana

    12 of 23

    Middle half

    Carbon
    52.2%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Carbon County

Starts at Carbon County's median, 4.2 pCi/L

4.2pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.2 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Carbon County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Carbon County, At a glance

Carbon County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Carbon County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: Moderate across 82% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Carbon County, 2008 to 2017, laboratory

Reported results by concentration band, Carbon County, 2008 to 2017, laboratory
Under 2 pCi/L: 13%2 to 4 pCi/L: 35%4 pCi/L and above: 52%

Of 46 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Carbon County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L613.0%
2 to 4 pCi/L1634.8%
4 pCi/L and above2452.2%
What these figures count

These are the 46 tests reported to CDC for Carbon County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Carbon County, Compared

Carbon County radon figures, compared

Calculated by Radon411

More than half: 52.2% of the 46 radon tests reported to CDC for Carbon County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 12th of 23 Montana counties with 30 or more tests for the same period. That is 6.7 points above the 45.5% pooled from 51 Montana counties.

The median result, 4.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 144.4 pCi/L. The rest split 13.0% under 2 pCi/L and 34.8% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 52.2% share point the same way here.

2 of its 5 bordering counties with figures ran higher, led by Park County at 60.0%; Big Horn County, WY reported 42.4%. Statewide for the same period, Richland County reported the highest share (78.6%) and Cascade County the lowest (29.4%).

CDC's ten-year totals for Carbon County went from 36 tests (2005 to 2014) to 46 (2008 to 2017), the share going from 50.0% to 52.2%.

Nationally, every county with a figure for the same period pools to 35.7%; Carbon County sits 16.5 points above it.

Carbon County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Carbon County
Carbon County4652.2%4.2 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled−6.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−16.5 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+26.4 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−22.8 points
Park County, MTborders it15060.0%5.3 pCi/L+7.8 points
Stillwater County, MTborders it5955.9%4.8 pCi/L+3.7 points
Park County, WYborders it50542.8%3.4 pCi/L−9.4 points
Yellowstone County, MTborders it1,52042.4%3.4 pCi/L−9.8 points
Big Horn County, WYborders it9942.4%3.5 pCi/L−9.8 points
Big Horn County, MTborders it2128.6%2.0 pCi/L−23.6 points
Where Carbon County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultCarbon County testsCarbon County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L613.0%29.2%39.6%−16.2 points
2 to 4 pCi/L1634.8%25.2%24.7%+9.6 points
4 pCi/L and above2452.2%45.5%35.7%+6.7 points
Carbon County ranked among the 23 Montana counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Lewis and Clark County7 of 2346861.8%5.1 pCi/L
Park County8 of 2315060.0%5.3 pCi/L
Beaverhead County9 of 233759.5%5.0 pCi/L
Mineral County10 of 233056.7%5.1 pCi/L
Stillwater County11 of 235955.9%4.8 pCi/L
Carbon County12 of 234652.2%4.2 pCi/L
Lincoln County13 of 237451.4%4.0 pCi/L
Madison County14 of 235850.0%3.9 pCi/L
Sanders County14 of 233850.0%4.0 pCi/L
Dawson County16 of 235947.5%3.5 pCi/L
Missoula County17 of 232,61344.6%3.4 pCi/L
Carbon County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20174652.2%4.2 pCi/L144.4 pCi/L45.5%−0.3 points
2007 to 20164052.5%4.0 pCi/L144.4 pCi/L46.6%Level
2006 to 20154052.5%4.0 pCi/L144.4 pCi/L47.4%+2.5 points
2005 to 20143650.0%4.0 pCi/L144.4 pCi/L48.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Carbon County, Geology

The ground under Carbon County

Predicted

Most of the ground under Carbon County is one class on USGS's geologic map: 82.0% of its land is moderate radon potential, with 18.0% high. The map puts 60.6% of Carbon County in the area it calls Plains and Mountains and 21.3% in Absaroka Volcanic Field, with one smaller area beside them. USGS gives both a radon index of 10, in the moderate band (9 to 11).

USGS's geologic areas under Carbon County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Plains and MountainsMarine and continental shale, siltstone, and sandstone of Cretaceous and Tertiary ages, and volcanic rocks.Moderate1060.6%
Absaroka Volcanic FieldIntrusive and extrusive volcanic rocks and overlying sediments.Moderate1021.3%
Big Horn MountainsGranitic and metamorphic rocks.High1317.6%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Carbon County beside the ground around it

Montana as a whole has more high-potential ground than Carbon County: 78.5% of its land, against 18.0% here. Of the 6 counties that border it, 3 have more high-potential ground, Big Horn County, WY the most at 100%.

Share of land by USGS radon potential: Carbon County, the 6 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Carbon CountyZone 1None82.0%18.0%
Stillwater CountyZone 1None100%None
Yellowstone CountyZone 2None100%None
Park County, WYZone 1None51.9%48.1%
Park CountyZone 1None99.3%0.7%
Big Horn County, WYZone 1NoneNone100%
Big Horn CountyZone 1None49.8%50.2%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

The map rates the ground, not the air in any home.

Local help

Carbon County, Local resources

Radon testing and mitigation in Carbon County

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

Carbon County, Questions

Questions about radon in Carbon County

Are radon levels high in Carbon County?

Over the 2008 to 2017 laboratory totals, 52.2% of the radon tests reported to CDC for Carbon County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.2 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 11 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Carbon County?

Carbon County borders 6 counties: Stillwater County, MT, Yellowstone County, MT, Park County, WY, Park County, MT, Big Horn County, WY and Big Horn County, MT.

Products

Carbon County, Products

Testing a home in Carbon County

In Carbon County, 52.2% of 46 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 45.5% pooled across Montana. In Zone 1 the year-round level in Carbon 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

Carbon County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Carbon County

Explore

Carbon County, Bordering counties

Counties bordering Carbon County

Calculated by Radon411

Carbon County, Cities and towns

Cities and towns in Carbon County

Carbon County is growing: the Census Bureau puts it at 11,466 residents on July 1, 2025, up 9.1% from 10,511 in 2020. Spread over its land, that is 5.6 people to the square mile. Its largest town, Red Lodge, has 2,723 residents, 23.7% of the total. Together its 5 incorporated places hold 39.9% of those residents; the other 60.1% live outside any of them. Reported testing is thin here: 46 tests over 2008 to 2017, or 4.0 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.6.

From Red Lodge to Bearcreek, CDC publishes no figure by town: each reads Carbon County's.

The cities and towns in Carbon County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Red Lodge2,723+19.9%23.7%
Bridger709+6.8%6.2%
Joliet613+5.5%5.3%
Fromberg422+7.1%3.7%
Bearcreek106+17.8%0.9%

5 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).

Carbon County, Homes

Homes in Carbon County

Carbon County is a place of houses on their own lots: 81% of its 6,431 homes are detached single-family houses, against 69% across Montana. Half of its homes were built before 1978, close to Montana's 1980: 32% date from before 1960 and 21% from 2000 or later. 74% 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 in Carbon County, Montana, 2019 to 2023
HomesCarbon CountyMontana
Housing units6,431522,939
Detached houses81%69%
In buildings of 5 or more3%9%
Mobile homes10%10%
Built before 196032%26%
Built since 200021%27%
Middle year built19781980
Owner-occupied74%69%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.