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Radon Levels in Beaverhead County, Montana

EPA puts Beaverhead County in Zone 1, its highest radon zone, and high results are common there: 59.5% of the 37 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

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  • Share at 4+ pCi/L

    59.5%

    14.0 pts above MT

    Beaverhead
    59.5%
    Montana
    45.5%

    37 tests, 2008 to 2017

  • Median result

    5.0pCi/L

    Action level reached

    Beaverhead
    5.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    37

    22nd of 23 by tests

    Beaverhead
    37
    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

    9 of 23

    Middle half

    Beaverhead
    59.5%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Beaverhead County

Starts at Beaverhead County's median, 5.0 pCi/L

5.0pCi/L

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

EPA’s reading of 5.0 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. Beaverhead County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Beaverhead County, At a glance

Beaverhead County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Beaverhead 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: High across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Beaverhead County, 2008 to 2017, laboratory
Under 2 pCi/L: 24%2 to 4 pCi/L: 16%4 pCi/L and above: 60%

Of 37 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Beaverhead County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L924.3%
2 to 4 pCi/L616.2%
4 pCi/L and above2259.5%
What these figures count

These are the 37 tests reported to CDC for Beaverhead 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

Beaverhead County, Compared

Beaverhead County radon figures, compared

Calculated by Radon411

More than half: 59.5% of the 37 radon tests reported to CDC for Beaverhead County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 9th of 23 Montana counties with 30 or more tests for the same period. That is 14.0 points above the 45.5% pooled from 51 Montana counties.

The median result, 5.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 36.1 pCi/L. The rest split 24.3% under 2 pCi/L and 16.2% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 59.5% share point the same way here.

2 of its 5 bordering counties with figures ran higher, led by Silver Bow County at 70.1%; Ravalli County reported 44.6%. 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 Beaverhead County went from 25 tests (2005 to 2014) to 37 (2008 to 2017), the share going from 56.0% to 59.5%.

Nationally, every county with a figure for the same period pools to 35.7%; Beaverhead County sits 23.8 points above it.

Beaverhead County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Beaverhead County
Beaverhead County3759.5%5.0 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled−14.0 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−23.8 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+19.1 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−30.1 points
Clark County, IDborders it475.0%14.1 pCi/L+15.5 points
Silver Bow County, MTborders it17470.1%6.0 pCi/L+10.6 points
Lemhi County, IDborders it11265.2%5.2 pCi/L+5.7 points
Madison County, MTborders it5850.0%3.9 pCi/L−9.5 points
Fremont County, IDborders it10149.5%3.9 pCi/L−10.0 points
Ravalli County, MTborders it1,09044.6%3.5 pCi/L−14.9 points
Deer Lodge County, MTborders it1330.8%3.4 pCi/L−28.7 points
Where Beaverhead County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultBeaverhead County testsBeaverhead County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L924.3%29.2%39.6%−4.9 points
2 to 4 pCi/L616.2%25.2%24.7%−9.0 points
4 pCi/L and above2259.5%45.5%35.7%+14.0 points
Beaverhead 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
Jefferson County4 of 236271.0%6.3 pCi/L
Silver Bow County5 of 2317470.1%6.0 pCi/L
Judith Basin County6 of 234264.3%5.9 pCi/L
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
Beaverhead County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20173759.5%5.0 pCi/L36.1 pCi/L45.5%+6.4 points
2007 to 20163253.1%4.1 pCi/L26.1 pCi/L46.6%−1.7 points
2006 to 20153154.8%4.2 pCi/L26.1 pCi/L47.4%−1.2 points
2005 to 20142556.0%4.2 pCi/L26.1 pCi/L48.0%First on file

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

Beaverhead County, Geology

The ground under Beaverhead County

Predicted

USGS's geologic map puts all of Beaverhead County's mapped land in one class: high radon potential. All of it lies in the area the map calls Northern Rocky Mountains, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Beaverhead County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High1399.8%

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

Beaverhead County beside the ground around it

Beaverhead County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 7 counties that border it, none has as large a share of high-potential ground; Deer Lodge County comes nearest at 100%.

Share of land by USGS radon potential: Beaverhead County, the 7 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Beaverhead CountyZone 1NoneNone100%
Lemhi County, IDZone 1NoneNone100%
Madison CountyZone 1NoneNone100%
Silver Bow CountyZone 1NoneNone100%
Deer Lodge CountyZone 1NoneNone100%
Clark County, IDZone 1None33.3%66.7%
Ravalli CountyZone 1NoneNone100%
Fremont County, IDZone 1None31.8%68.2%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Beaverhead County, Local resources

Radon testing and mitigation in Beaverhead 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

Beaverhead County, Questions

Questions about radon in Beaverhead County

Are radon levels high in Beaverhead County?

Over the 2008 to 2017 laboratory totals, 59.5% of the radon tests reported to CDC for Beaverhead County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.0 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 8 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Beaverhead County?

Beaverhead County borders 7 counties: Lemhi County, ID, Madison County, MT, Silver Bow County, MT, Deer Lodge County, MT, Clark County, ID, Ravalli County, MT and Fremont County, ID.

Products

Beaverhead County, Products

Testing a home in Beaverhead County

In Beaverhead County, 59.5% of 37 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 Beaverhead 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

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

Explore

Beaverhead County, Bordering counties

Counties bordering Beaverhead County

Calculated by Radon411

Beaverhead County, Cities and towns

Cities and towns in Beaverhead County

Beaverhead County is growing: the Census Bureau puts it at 10,043 residents on July 1, 2025, up 7.1% from 9,375 in 2020. Spread over its land, that is 1.8 people to the square mile. Its largest town, Dillon, has 4,271 residents, 42.5% of the total. Together its 2 incorporated places hold 44.7% of those residents; the other 55.3% live outside any of them. Reported testing is thin here: 37 tests over 2008 to 2017, or 3.7 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.6.

From Dillon to Lima, CDC publishes no figure by town: each reads Beaverhead County's.

The cities and towns in Beaverhead County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Dillon4,271+10.0%42.5%
Lima221+5.7%2.2%

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).

Beaverhead County, Homes

Homes in Beaverhead County

Of Beaverhead County's 4,973 homes, 71% are detached houses, against 69% across Montana; 18% are mobile homes. Half of its homes were built before 1980, close to Montana's 1980: 25% date from before 1960 and 22% from 2000 or later. 67% 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 Beaverhead County, Montana, 2019 to 2023
HomesBeaverhead CountyMontana
Housing units4,973522,939
Detached houses71%69%
In buildings of 5 or more4%9%
Mobile homes18%10%
Built before 196025%26%
Built since 200022%27%
Middle year built19801980
Owner-occupied67%69%

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