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Radon Levels in Missoula County, Montana

EPA puts Missoula County in Zone 1, its highest radon zone, and high results are common there: 44.6% of the 2,613 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

    44.6%

    0.9 pts below MT

    Missoula
    44.6%
    Montana
    45.5%

    2,613 tests, 2008 to 2017

  • Median result

    3.4pCi/L

    Below action level

    Missoula
    3.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    2,613

    Most tested in Montana

    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

    17 of 23

    Middle half

    Missoula
    44.6%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Missoula County

Starts at Missoula County's median, 3.4 pCi/L

3.4pCi/L

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

EPA’s reading of 3.4 pCi/L

Between 2 and 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Missoula County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Missoula County, At a glance

Missoula County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Missoula 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 Missoula County, 2008 to 2017, laboratory

Reported results by concentration band, Missoula County, 2008 to 2017, laboratory
Under 2 pCi/L: 30%2 to 4 pCi/L: 25%4 pCi/L and above: 45%

Of 2,613 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Missoula County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L79430.4%
2 to 4 pCi/L65325.0%
4 pCi/L and above1,16644.6%
What these figures count

These are the 2,613 tests reported to CDC for Missoula 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

Missoula County, Compared

Missoula County radon figures, compared

Calculated by Radon411

In Missoula County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (1,166 of 2,613) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 8.9 points higher. Across 51 Montana counties pooled together, 45.5% of tests reached that level, so Missoula County runs 0.9 points below its state.

Of 7 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 30.3% (Clearwater County, ID) to 56.7% (Mineral County). By share, Missoula County is 17th of 23 Montana counties with 30 or more tests for the same period.

Half the tests came in under 3.4 pCi/L and half over it; the single highest reached 202.8 pCi/L. Below the action level, 794 tests (30.4%) came in under 2 pCi/L, against 29.2% statewide, and 653 tests (25.0%) fell between 2 and 4, against 25.2% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 44.6% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 113 tests taken after mitigation in Missoula County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Missoula County went from 1,903 tests (2005 to 2014) to 2,613 (2008 to 2017), the share going from 49.2% to 44.6%.

Missoula County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Missoula County
Missoula County2,61344.6%3.4 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled+0.9 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−8.9 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+34.0 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−15.2 points
Powell County, MTborders it2958.6%4.2 pCi/L+14.0 points
Mineral County, MTborders it3056.7%5.1 pCi/L+12.1 points
Sanders County, MTborders it3850.0%4.0 pCi/L+5.4 points
Ravalli County, MTborders it1,09044.6%3.5 pCi/LLevel
Lake County, MTborders it14940.3%2.9 pCi/L−4.3 points
Idaho County, IDborders it9040.0%2.9 pCi/L−4.6 points
Flathead County, MTborders it89137.8%3.0 pCi/L−6.8 points
Clearwater County, IDborders it3330.3%1.8 pCi/L−14.3 points
Granite County, MTborders it825.0%2.1 pCi/L−19.6 points
Where Missoula County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultMissoula County testsMissoula County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L79430.4%29.2%39.6%+1.2 points
2 to 4 pCi/L65325.0%25.2%24.7%−0.2 points
4 pCi/L and above1,16644.6%45.5%35.7%−0.9 points
Missoula 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
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
Ravalli County18 of 231,09044.6%3.5 pCi/L
Gallatin County19 of 231,60042.8%3.2 pCi/L
Yellowstone County20 of 231,52042.4%3.4 pCi/L
Lake County21 of 2314940.3%2.9 pCi/L
Flathead County22 of 2389137.8%3.0 pCi/L
Missoula County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20172,61344.6%3.4 pCi/L202.8 pCi/L45.5%−2.6 points
2007 to 20162,36547.2%3.7 pCi/L202.8 pCi/L46.6%−1.6 points
2006 to 20152,12248.8%3.9 pCi/L202.8 pCi/L47.4%−0.4 points
2005 to 20141,90349.2%3.9 pCi/L202.8 pCi/L48.0%First on file

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

Missoula County, Geology

The ground under Missoula County

Predicted

USGS's geologic map puts all of Missoula 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 Missoula County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High1399.9%

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

Missoula County beside the ground around it

Missoula County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 9 counties that border it, none has as large a share of high-potential ground; Flathead County comes nearest at 100%.

Share of land by USGS radon potential: Missoula County, the 9 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Missoula CountyZone 1NoneNone100%
Lake CountyZone 1NoneNone100%
Powell CountyZone 1NoneNone100%
Mineral CountyZone 1NoneNone100%
Granite CountyZone 1NoneNone100%
Sanders CountyZone 1NoneNone100%
Ravalli CountyZone 1NoneNone100%
Flathead CountyZone 1NoneNone100%
Clearwater County, IDZone 118.8%None81.2%
Idaho County, IDZone 120.7%0.1%79.3%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Missoula County, Local resources

Radon testing and mitigation in Missoula 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

Missoula County, Questions

Questions about radon in Missoula County

Are radon levels high in Missoula County?

Over the 2008 to 2017 laboratory totals, 44.6% of the radon tests reported to CDC for Missoula County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.4 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 16 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Missoula County?

Missoula County borders 9 counties: Lake County, MT, Powell County, MT, Mineral County, MT, Granite County, MT, Sanders County, MT, Ravalli County, MT, Flathead County, MT, Clearwater County, ID and Idaho County, ID.

Products

Missoula County, Products

Testing a home in Missoula County

In Missoula County, 44.6% of 2,613 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 Missoula 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

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

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Missoula County, Bordering counties

Counties bordering Missoula County

Calculated by Radon411

Missoula County, Cities and towns

Cities and towns in Missoula County

The Census Bureau estimates 123,513 residents in Missoula County for July 1, 2025, 5,176 more than in 2020 (+4.4%). That works out to 48 people per square mile of land. Missoula, its one incorporated place, has 78,903 residents, 63.9% of the total. Testing is reported here more often than across the state: CDC's 2,613 reported tests for 2008 to 2017 come to 21.2 for every 1,000 residents (2025 estimate), against 8.6 for Montana.

Missoula is the one incorporated place here; CDC publishes no figure by town, so it reads Missoula County's.

Missoula, Missoula County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Missoula78,903+6.0%63.9%

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).

Missoula County, Homes

Homes in Missoula County

Of Missoula County's 56,008 homes, 58% are detached houses, against 69% across Montana; 18% are in buildings of five or more homes. Half of its homes were built before 1984, close to Montana's 1980: 21% date from before 1960 and 30% from 2000 or later. 60% 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 Missoula County, Montana, 2019 to 2023
HomesMissoula CountyMontana
Housing units56,008522,939
Detached houses58%69%
In buildings of 5 or more18%9%
Mobile homes9%10%
Built before 196021%26%
Built since 200030%27%
Middle year built19841980
Owner-occupied60%69%

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