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Radon Levels in Yellowstone County, Montana

EPA puts Yellowstone County in Zone 2, its middle radon zone, and high results are common there: 42.4% of the 1,520 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

    42.4%

    3.1 pts below MT

    Yellowstone
    42.4%
    Montana
    45.5%

    1,520 tests, 2008 to 2017

  • Median result

    3.4pCi/L

    Below action level

    Yellowstone
    3.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,520

    3rd of 23 by tests

    Yellowstone
    1,520
    Missoula
    2,613

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Montana

    20 of 23

    Lowest quarter

    Yellowstone
    42.4%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Yellowstone County

Starts at Yellowstone 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. Yellowstone County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Yellowstone County, At a glance

Yellowstone County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Yellowstone County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Yellowstone County, 2008 to 2017, laboratory
Under 2 pCi/L: 22%2 to 4 pCi/L: 36%4 pCi/L and above: 42%

Of 1,520 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Yellowstone County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L33422.0%
2 to 4 pCi/L54135.6%
4 pCi/L and above64542.4%
What these figures count

These are the 1,520 tests reported to CDC for Yellowstone 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

Yellowstone County, Compared

Yellowstone County radon figures, compared

Calculated by Radon411

In Yellowstone County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (645 of 1,520) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 6.7 points higher. Across 51 Montana counties pooled together, 45.5% of tests reached that level, so Yellowstone County runs 3.1 points below its state.

Of 2 neighbours with a figure, all 2 reported a larger share at or above 4 pCi/L; the spread is 52.2% (Carbon County) to 55.9% (Stillwater County). By share, Yellowstone County is 20th 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 59.2 pCi/L. Below the action level, 334 tests (22.0%) came in under 2 pCi/L, against 29.2% statewide, and 541 tests (35.6%) fell between 2 and 4, against 25.2% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 42.4% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential. CDC also counts 174 tests taken after mitigation in Yellowstone County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Yellowstone County went from 1,273 tests (2005 to 2014) to 1,520 (2008 to 2017), the share going from 43.2% to 42.4%.

Yellowstone County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Yellowstone County
Yellowstone County1,52042.4%3.4 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled+3.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−6.7 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+36.2 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−13.0 points
Treasure County, MTborders it1100.0%7.5 pCi/L+57.6 points
Stillwater County, MTborders it5955.9%4.8 pCi/L+13.5 points
Carbon County, MTborders it4652.2%4.2 pCi/L+9.8 points
Rosebud County, MTborders it540.0%2.9 pCi/L−2.4 points
Musselshell County, MTborders it1729.4%2.6 pCi/L−13.0 points
Big Horn County, MTborders it2128.6%2.0 pCi/L−13.8 points
Where Yellowstone County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultYellowstone County testsYellowstone County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L33422.0%29.2%39.6%−7.2 points
2 to 4 pCi/L54135.6%25.2%24.7%+10.4 points
4 pCi/L and above64542.4%45.5%35.7%−3.1 points
Yellowstone 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
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
Cascade County23 of 2323529.4%1.7 pCi/L
Yellowstone County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20171,52042.4%3.4 pCi/L59.2 pCi/L45.5%−1.1 points
2007 to 20161,48243.5%3.5 pCi/L136.7 pCi/L46.6%+0.4 points
2006 to 20151,42143.1%3.5 pCi/L136.7 pCi/L47.4%−0.1 points
2005 to 20141,27343.2%3.5 pCi/L136.7 pCi/L48.0%First on file

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

Yellowstone County, Geology

The ground under Yellowstone County

Predicted

USGS's geologic map puts all of Yellowstone County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Plains and Mountains, to which USGS gives a radon index of 10, in the moderate band (9 to 11).

USGS's geologic areas under Yellowstone 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.Moderate10100%

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

Yellowstone County beside the ground around it

Across Montana 78.5% of the land is rated high; none of Yellowstone County's is. Of the 7 counties that border it, 6 have more high-potential ground, Rosebud County the most at 56.2%.

Share of land by USGS radon potential: Yellowstone County, the 7 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Yellowstone CountyZone 2None100%None
Musselshell CountyZone 2None99.4%0.6%
Stillwater CountyZone 1None100%None
Golden Valley CountyZone 2None91.6%8.4%
Big Horn CountyZone 1None49.8%50.2%
Treasure CountyZone 2None73.5%26.5%
Carbon CountyZone 1None82.0%18.0%
Rosebud CountyZone 1None43.8%56.2%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Yellowstone County, Local resources

Radon testing and mitigation in Yellowstone 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

Yellowstone County, Questions

Questions about radon in Yellowstone County

Are radon levels high in Yellowstone County?

Over the 2008 to 2017 laboratory totals, 42.4% of the radon tests reported to CDC for Yellowstone 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, 19 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Yellowstone County?

Yellowstone County borders 7 counties: Musselshell County, Stillwater County, Golden Valley County, Big Horn County, Treasure County, Carbon County and Rosebud County.

Products

Yellowstone County, Products

Testing a home in Yellowstone County

In Yellowstone County, 42.4% of 1,520 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 45.5% pooled across Montana. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Yellowstone County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Yellowstone County homes, compared

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Yellowstone County, Bordering counties

Counties bordering Yellowstone County

Calculated by Radon411

Yellowstone County, Cities and towns

Cities and towns in Yellowstone County

The Census Bureau estimates 172,692 residents in Yellowstone County for July 1, 2025, 7,484 more than in 2020 (+4.5%). That works out to 66 people per square mile of land. Billings alone is home to 121,239 of them, 70.2% of the total. Together its 3 incorporated places hold 74.5% of those residents; the other 25.5% live outside any of them. CDC's 1,520 reported tests for 2008 to 2017 work out to 8.8 per 1,000 residents (2025 estimate), close to Montana's 8.6.

From Billings to Broadview, CDC publishes no figure by town: each reads Yellowstone County's.

The cities and towns in Yellowstone County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Billings121,239+3.4%70.2%
Laurel7,205−0.2%4.2%
Broadview136−2.2%Under 0.1%

3 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).

Yellowstone County, Homes

Homes in Yellowstone County

Of Yellowstone County's 73,363 homes, 66% are detached houses, against 69% across Montana; 11% are in buildings of five or more homes. Half of its homes were built before 1982, close to Montana's 1980: 23% date from before 1960 and 27% from 2000 or later. 69% 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 Yellowstone County, Montana, 2019 to 2023
HomesYellowstone CountyMontana
Housing units73,363522,939
Detached houses66%69%
In buildings of 5 or more11%9%
Mobile homes10%10%
Built before 196023%26%
Built since 200027%27%
Middle year built19821980
Owner-occupied69%69%

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