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Radon Levels in Silver Bow County, Montana

EPA puts Silver Bow County in Zone 1, its highest radon zone, and high results are common there: 70.1% of the 174 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

    70.1%

    24.6 pts above MT

    Silver Bow
    70.1%
    Montana
    45.5%

    174 tests, 2008 to 2017

  • Median result

    6.0pCi/L

    Action level reached

    Silver Bow
    6.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    174

    8th of 23 by tests

    Silver Bow
    174
    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

    5 of 23

    Top quarter

    Silver Bow
    70.1%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Silver Bow County

Starts at Silver Bow County's median, 6.0 pCi/L

6.0pCi/L

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

EPA’s reading of 6.0 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. Silver Bow County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Silver Bow County, At a glance

Silver Bow County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Silver Bow 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 Silver Bow County, 2008 to 2017, laboratory

Reported results by concentration band, Silver Bow County, 2008 to 2017, laboratory
Under 2 pCi/L: 13%2 to 4 pCi/L: 17%4 pCi/L and above: 70%

Of 174 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Silver Bow County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2313.2%
2 to 4 pCi/L2916.7%
4 pCi/L and above12270.1%
What these figures count

These are the 174 tests reported to CDC for Silver Bow 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

Silver Bow County, Compared

Silver Bow County radon figures, compared

Calculated by Radon411

More than half: 70.1% of the 174 radon tests reported to CDC for Silver Bow County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 5th of 23 Montana counties with 30 or more tests for the same period. That is 24.6 points above the 45.5% pooled from 51 Montana counties.

The median result, 6.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 48.5 pCi/L. The rest split 13.2% under 2 pCi/L and 16.7% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 70.1% share point the same way here.

1 of its 3 bordering counties with figures ran higher, led by Jefferson County at 71.0%; Madison County reported 50.0%. 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 Silver Bow County went from 181 tests (2005 to 2014) to 174 (2008 to 2017), the share going from 68.0% to 70.1%.

Nationally, every county with a figure for the same period pools to 35.7%; Silver Bow County sits 34.4 points above it. CDC also counts 6 tests taken after mitigation in Silver Bow County for the same period: tests in homes where a fix was already in.

Silver Bow County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Silver Bow County
Silver Bow County17470.1%6.0 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled−24.6 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−34.4 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+8.5 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−40.7 points
Jefferson County, MTborders it6271.0%6.3 pCi/L+0.9 points
Beaverhead County, MTborders it3759.5%5.0 pCi/L−10.6 points
Madison County, MTborders it5850.0%3.9 pCi/L−20.1 points
Deer Lodge County, MTborders it1330.8%3.4 pCi/L−39.3 points
Where Silver Bow County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultSilver Bow County testsSilver Bow County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L2313.2%29.2%39.6%−16.0 points
2 to 4 pCi/L2916.7%25.2%24.7%−8.5 points
4 pCi/L and above12270.1%45.5%35.7%+24.6 points
Silver Bow 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
Richland County1 of 234278.6%5.9 pCi/L
Sheridan County2 of 237075.7%6.5 pCi/L
Fergus County3 of 237672.4%7.2 pCi/L
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
Silver Bow County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 201717470.1%6.0 pCi/L48.5 pCi/L45.5%+1.1 points
2007 to 201618469.0%6.0 pCi/L48.5 pCi/L46.6%+0.1 points
2006 to 201519368.9%6.0 pCi/L48.7 pCi/L47.4%+0.9 points
2005 to 201418168.0%5.8 pCi/L48.7 pCi/L48.0%First on file

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

Silver Bow County, Geology

The ground under Silver Bow County

Predicted

USGS's geologic map puts all of Silver Bow 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 Silver Bow County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High13100%

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

Silver Bow County beside the ground around it

Silver Bow County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 4 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: Silver Bow County, the 4 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Silver Bow CountyZone 1NoneNone100%
Deer Lodge CountyZone 1NoneNone100%
Jefferson CountyZone 1NoneNone100%
Beaverhead CountyZone 1NoneNone100%
Madison CountyZone 1NoneNone100%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Silver Bow County, Local resources

Radon testing and mitigation in Silver Bow 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

Silver Bow County, Questions

Questions about radon in Silver Bow County

Are radon levels high in Silver Bow County?

Over the 2008 to 2017 laboratory totals, 70.1% of the radon tests reported to CDC for Silver Bow County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.0 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 4 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Silver Bow County?

Silver Bow County borders 4 counties: Deer Lodge County, Jefferson County, Beaverhead County and Madison County.

Products

Silver Bow County, Products

Testing a home in Silver Bow County

In Silver Bow County, 70.1% of 174 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 Silver Bow 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

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

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Silver Bow County, Bordering counties

Counties bordering Silver Bow County

Calculated by Radon411

Silver Bow County, Cities and towns

Cities and towns in Silver Bow County

The Census Bureau estimates 36,118 residents in Silver Bow County for July 1, 2025, 910 more than in 2020 (+2.6%). That works out to 50 people per square mile of land. Butte-Silver Bow alone is home to 35,469 of them, 98.2% of the total. Its 2 incorporated places account for all of those residents. Reported testing is thin here: 174 tests over 2008 to 2017, or 4.8 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.6.

From Butte-Silver Bow to Walkerville, CDC publishes no figure by town: each reads Silver Bow County's.

The cities and towns in Silver Bow County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Butte-Silver Bow35,469+2.6%98.2%
Walkerville649+2.4%1.8%

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).

Silver Bow County, Homes

Homes in Silver Bow County

Of Silver Bow County's 17,396 homes, 72% are detached houses, against 69% across Montana; 11% are in buildings of five or more homes. The homes are older than Montana's as a whole: half were built before 1956 (1980 for Montana), and 55% date from before 1960. 70% 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 Silver Bow County, Montana, 2019 to 2023
HomesSilver Bow CountyMontana
Housing units17,396522,939
Detached houses72%69%
In buildings of 5 or more11%9%
Mobile homes6%10%
Built before 196055%26%
Built since 200012%27%
Middle year built19561980
Owner-occupied70%69%

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