Skip to content
RADON411

Locations and reports

Montana Radon Map and Levels by County

Montana's counties span EPA Zones 1 and 2. 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

    45.5%

    9.8 pts above U.S.

    Montana
    45.5%
    U.S.
    35.7%

    9,893 tests across 51 counties, 2008 to 2017

  • Rank among states

    8 of 47

    Ten highest states

    Montana
    45.5%
    North Dakota
    59.3%

    By share, every state pooled the same way, 2008 to 2017

  • Counties in EPA Zone 1

    49 of 56

    Most at highest potential

    Zone 1
    49
    Zone 2
    7

    Most counties sit in Zone 1; Zone 1 is the highest potential

  • Highest county

    78.6%

    Richland County

    Richland
    78.6%
    Cascade
    29.4%

    Counties with 30+ tests, 2008 to 2017

Read a result for Montana

Starts at EPA's action level

4.0pCi/L

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

EPA’s reading of 4.0 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. 45.5% of Montana's reported tests reached 4 pCi/L, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Montana, At a glance

Montana at a glance

Predicted: EPA radon zone

56 of 56 counties classified

EPA classifies counties, not states. Of the 56 counties in Montana with a zone, 49 are in Zone 1 and 7 in Zone 2.

  • Zone 1: Highest predicted potentialgreater than 4 pCi/L49 of 56 counties · 87.5%
  • Zone 2: Moderate predicted potential2 to 4 pCi/L7 of 56 counties · 12.5%

An EPA radon zone predicts a whole county. It is not intended to determine whether any individual home should be tested: homes with elevated levels occur in all three zones, and EPA recommends testing every home regardless of zone.

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

CDC test figures, county by county

CDC publishes Montana's radon test figures by county: 53 of its 56 counties have one. Each one's share is in the county list.

How to read these figures

Montana, Compared

Montana radon figures, compared

Calculated by Radon411
Montana, 2008 to 2017, laboratory
45.5%
of 9,893 tests at or above 4 pCi/L, pooled
Against the U.S.
+9.8points
35.7% pooled
Rank among the states
8 of 47
1 is the highest share
Counties with 30 or more tests
23
Highest
78.6%
Richland County
Lowest
29.4%
Cascade County

Pooled across 51 counties, 45.5% of the 9,893 radon tests reported to CDC for Montana over the 2008 to 2017 laboratory totals were at or above 4 pCi/L: close to half or more. That is 8th of 47 states with county figures for the period; Wisconsin (46.9%) above it and Wyoming (44.3%) below.

Its 23 counties with 30 or more tests run from 29.4% in Cascade County to 78.6% in Richland County; in 15 of them half or more of the reported tests reached 4 pCi/L. By band, 15 counties at 50% or more, 7 counties at 30% to 50%, 1 county at 15% to 30%.

The national pool for the same period is 35.7%, so Montana runs 9.8 points above the country. EPA's 1993 map puts 49 of its 56 classified counties in Zone 1; the tests reported since bear that out at 45.5%.

Across its 4 overlapping ten-year totals, the share went from 48.0% (2005 to 2014) to 45.5% (2008 to 2017), down 2.5 points, with 2005 to 2014 the highest at 48.0%.

Montana ranked among 47 states by pooled share of tests at or above 4 pCi/L, 2008 to 2017, laboratory
StateRankCountiesTestsAt or above 4 pCi/L
South Dakota3 of 47626,27558.5%
Iowa4 of 479995,24558.5%
Ohio5 of 478898,84052.3%
Colorado6 of 476396,36747.0%
Wisconsin7 of 477268,10446.9%
Montana8 of 47519,89345.5%
Wyoming9 of 47237,63844.3%
Kentucky10 of 4712028,79343.7%
Minnesota11 of 4787130,91243.4%
Illinois12 of 47102108,90943.1%
Utah13 of 472828,34241.9%
Montana's highest and lowest counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/L
Richland County1 of 234278.6%
Sheridan County2 of 237075.7%
Fergus County3 of 237672.4%
Jefferson County4 of 236271.0%
Silver Bow County5 of 2317470.1%
Judith Basin County6 of 234264.3%
Lewis and Clark County7 of 2346861.8%
Park County8 of 2315060.0%
Beaverhead County9 of 233759.5%
Mineral County10 of 233056.7%
Cascade County23 of 2323529.4%
Flathead County22 of 2389137.8%
Lake County21 of 2314940.3%
Yellowstone County20 of 231,52042.4%
Gallatin County19 of 231,60042.8%
Montana's counties with 30 or more tests, by their own share at or above 4 pCi/L, 2008 to 2017, laboratory
ShareCountiesTheir testsFor example
50% or more151,426Richland County, Sheridan County, Fergus County
30% to 50%77,922Dawson County, Missoula County, Ravalli County
15% to 30%1235Cascade County
5% to 15%00None
Under 5%00None
Montana ten-year laboratory totals, pooled, against the United States
PeriodCountiesTestsAt or above 4 pCi/LUnited StatesChange from the row before
2008 to 2017519,89345.5%35.7%−1.0 points
2007 to 2016519,30546.6%35.8%−0.8 points
2006 to 2015528,56047.4%36.3%−0.6 points
2005 to 2014527,67948.0%36.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period. CDC publishes no state or national figure.

Montana, Counties

Montana counties by EPA zone

Predicted

All 56 counties, grouped by the zone EPA predicts and ordered by their reported share at or above 4 pCi/L, under Montana's map. Each county has a page of its own.

Montana radon map by county: EPA radon zones. Map of Montana's 56 counties shaded by EPA radon zone: Zone 1 in red-orange, Zone 2 in amber. 49 in Zone 1, 7 in Zone 2, 0 in Zone 3.
Montana radon map by countyEPA radon zones for Montana's counties: 49 counties in Zone 1, 7 counties in Zone 2, 0 counties in Zone 3.A prediction for each county, not a reading of any home; elevated homes occur in all three zones.

The 12 highest in Montana, 2008 to 2017

Zone 1: highest predicted potential49

Local help

Montana, Local resources

Local resources in Montana

Who to ask in Montana: its radon program, test kits and professionals.

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

Montana, Questions

Questions about radon in Montana

Is radon a problem in Montana?

Of the 56 counties in Montana that EPA's Map of Radon Zones classifies, 49 carry Zone 1 (the highest predicted potential), 7 Zone 2 and 0 Zone 3. Pooled from 51 counties, 45.5% of the 9,893 radon tests reported to CDC over the 2008 to 2017 laboratory totals were at or above 4 pCi/L, 8th of 47 states.

Which Montana counties are in EPA radon Zone 1?

Zone 1 holds 49 counties in Montana; the first 8 by name are Beaverhead County, Big Horn County, Blaine County, Broadwater County, Carbon County, Carter County, Cascade County, Chouteau County, the rest in the county table on this page.

Which Montana counties have the highest radon?

Richland County 78.6% (42 tests) leads Montana by the share of reported tests at or above 4 pCi/L, 2008 to 2017, laboratory, then Sheridan County 75.7% (70 tests), Fergus County 72.4% (76 tests), Jefferson County 71.0% (62 tests), Silver Bow County 70.1% (174 tests).

Which EPA region is Montana in?

Montana is in EPA Region 8: Mountains and Plains.

Products

Montana, Products

Testing a home in Montana

45.5% of the 9,893 tests reported to CDC for Montana over the 2008 to 2017 laboratory totals reached 4 pCi/L: a short-term kit (2 to 90 days) gives a first answer in days, a long-term test the year-round average. A short-term kit (2 to 90 days) is the quick first check for a home in Montana; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Montana homes, compared

Explore

Cities in Montana with their own page

Radon data is published by county, not by city. Each city page sets the figures of the counties the city lies in side by side.