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Radon Levels in Gallatin County, Montana

EPA puts Gallatin County in Zone 1, its highest radon zone, and high results are common there: 42.8% of the 1,600 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

    42.8%

    2.7 pts below MT

    Gallatin
    42.8%
    Montana
    45.5%

    1,600 tests, 2008 to 2017

  • Median result

    3.2pCi/L

    Below action level

    Gallatin
    3.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,600

    2nd of 23 by tests

    Gallatin
    1,600
    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

    19 of 23

    Lowest quarter

    Gallatin
    42.8%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Gallatin County

Starts at Gallatin County's median, 3.2 pCi/L

3.2pCi/L

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

EPA’s reading of 3.2 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. Gallatin County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Gallatin County, At a glance

Gallatin County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Gallatin 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 79% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Gallatin County, 2008 to 2017, laboratory
Under 2 pCi/L: 36%2 to 4 pCi/L: 21%4 pCi/L and above: 43%

Of 1,600 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Gallatin County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L57636.0%
2 to 4 pCi/L34021.3%
4 pCi/L and above68442.8%
What these figures count

These are the 1,600 tests reported to CDC for Gallatin 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

Gallatin County, Compared

Gallatin County radon figures, compared

Calculated by Radon411

In Gallatin County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (684 of 1,600) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 7.1 points higher. Across 51 Montana counties pooled together, 45.5% of tests reached that level, so Gallatin County runs 2.7 points below its state.

Of 6 neighbours with a figure, all 6 reported a larger share at or above 4 pCi/L; the spread is 42.8% (Park County, WY) to 71.0% (Jefferson County). By share, Gallatin County is 19th of 23 Montana counties with 30 or more tests for the same period.

Half the tests came in under 3.2 pCi/L and half over it; the single highest reached 131.2 pCi/L. Below the action level, 576 tests (36.0%) came in under 2 pCi/L, against 29.2% statewide, and 340 tests (21.3%) fell between 2 and 4, against 25.2% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 42.8% share point the same way here. USGS geology rates 79% of the county's land high radon potential. CDC also counts 169 tests taken after mitigation in Gallatin County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Gallatin County went from 609 tests (2005 to 2014) to 1,600 (2008 to 2017), the share going from 53.7% to 42.8%.

Gallatin County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Gallatin County
Gallatin County1,60042.8%3.2 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled+2.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−7.1 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+35.8 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−13.4 points
Jefferson County, MTborders it6271.0%6.3 pCi/L+28.2 points
Park County, MTborders it15060.0%5.3 pCi/L+17.2 points
Broadwater County, MTborders it2556.0%4.1 pCi/L+13.2 points
Madison County, MTborders it5850.0%3.9 pCi/L+7.2 points
Fremont County, IDborders it10149.5%3.9 pCi/L+6.7 points
Teton County, WYborders it27844.6%3.4 pCi/L+1.8 points
Park County, WYborders it50542.8%3.4 pCi/LLevel
Meagher County, MTborders it10.0%3.6 pCi/L−42.8 points
Where Gallatin County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultGallatin County testsGallatin County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L57636.0%29.2%39.6%+6.8 points
2 to 4 pCi/L34021.3%25.2%24.7%−3.9 points
4 pCi/L and above68442.8%45.5%35.7%−2.7 points
Gallatin 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
Gallatin County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20171,60042.8%3.2 pCi/L131.2 pCi/L45.5%−1.7 points
2007 to 20161,29044.5%3.4 pCi/L131.2 pCi/L46.6%−4.3 points
2006 to 201591448.8%3.8 pCi/L120.9 pCi/L47.4%−4.9 points
2005 to 201460953.7%4.4 pCi/L120.9 pCi/L48.0%First on file

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

Gallatin County, Geology

The ground under Gallatin County

Predicted

Most of the ground under Gallatin County is one class on USGS's geologic map: 79.0% of its land is high radon potential, with 21.0% moderate. The map puts 71.4% of Gallatin County in the area it calls Northern Rocky Mountains and 14.3% in Plains and Mountains, with 2 smaller areas beside them. USGS gives the first a radon index of 13, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Gallatin County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High1371.4%
Plains and MountainsMarine and continental shale, siltstone, and sandstone of Cretaceous and Tertiary ages, and volcanic rocks.Moderate1014.3%
Middle Rocky Mts./YellowstoneExtrusive volcanics, rhyolite flows, variable composition.High127.6%
Absaroka Volcanic FieldIntrusive and extrusive volcanic rocks and overlying sediments.Moderate106.8%

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

Gallatin County beside the ground around it

On high-potential ground Gallatin County is close to Montana as a whole: 79.0% of its land against 78.5%. Of the 8 counties that border it, 3 have more high-potential ground, Broadwater County the most at 100%.

Share of land by USGS radon potential: Gallatin County, the 8 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Gallatin CountyZone 1None21.0%79.0%
Madison CountyZone 1NoneNone100%
Park CountyZone 1None99.3%0.7%
Fremont County, IDZone 1None31.8%68.2%
Broadwater CountyZone 1NoneNone100%
Jefferson CountyZone 1NoneNone100%
Meagher CountyZone 1None21.7%78.3%
Teton County, WYZone 1None58.3%41.7%
Park County, WYZone 1None51.9%48.1%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Gallatin County, Local resources

Radon testing and mitigation in Gallatin 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

Gallatin County, Questions

Questions about radon in Gallatin County

Are radon levels high in Gallatin County?

Over the 2008 to 2017 laboratory totals, 42.8% of the radon tests reported to CDC for Gallatin County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.2 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 18 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Gallatin County?

Gallatin County borders 8 counties: Madison County, MT, Park County, MT, Fremont County, ID, Broadwater County, MT, Jefferson County, MT, Meagher County, MT, Teton County, WY and Park County, WY.

Products

Gallatin County, Products

Testing a home in Gallatin County

In Gallatin County, 42.8% of 1,600 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 Gallatin 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

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

Explore

Gallatin County, Bordering counties

Counties bordering Gallatin County

Calculated by Radon411

Gallatin County, Cities and towns

Cities and towns in Gallatin County

Gallatin County is growing: the Census Bureau puts it at 128,740 residents on July 1, 2025, up 7.6% from 119,593 in 2020. That works out to 49 people per square mile of land. Its largest town, Bozeman, has 58,814 residents, 45.7% of the total. Together its 5 incorporated places hold 59.9% of those residents; the other 40.1% live outside any of them. CDC's 1,600 reported tests for 2008 to 2017 work out to 12.4 per 1,000 residents (2025 estimate), close to Montana's 8.6.

From Bozeman to West Yellowstone, CDC publishes no figure by town: each reads Gallatin County's.

The cities and towns in Gallatin County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Bozeman58,814+9.1%45.7%
Belgrade13,107+22.6%10.2%
Manhattan2,073−0.8%1.6%
Three Forks1,920−3.1%1.5%
West Yellowstone1,191−6.8%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).

Gallatin County, Homes

Homes in Gallatin County

Of Gallatin County's 55,589 homes, 60% are detached houses, against 69% across Montana; 14% are in buildings of five or more homes. Much of Gallatin County is recent building: 45% of its homes have gone up since 2000 and the middle year built is 1997, against 1980 for Montana. 62% 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 Gallatin County, Montana, 2019 to 2023
HomesGallatin CountyMontana
Housing units55,589522,939
Detached houses60%69%
In buildings of 5 or more14%9%
Mobile homes6%10%
Built before 196013%26%
Built since 200045%27%
Middle year built19971980
Owner-occupied62%69%

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