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Radon Levels in Richland County, Montana

EPA puts Richland County in Zone 1, its highest radon zone, and high results are common there: 78.6% of the 42 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

    78.6%

    33.1 pts above MT

    Richland
    78.6%
    Montana
    45.5%

    42 tests, 2008 to 2017

  • Median result

    5.9pCi/L

    Action level reached

    Richland
    5.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    42

    19th of 23 by tests

    Richland
    42
    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

    1 of 23

    Top quarter

    Richland
    78.6%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Richland County

Starts at Richland County's median, 5.9 pCi/L

5.9pCi/L

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

EPA’s reading of 5.9 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. Richland County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Richland County, At a glance

Richland County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Richland County, 2008 to 2017, laboratory
Under 2 pCi/L: 7%2 to 4 pCi/L: 14%4 pCi/L and above: 79%

Of 42 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Richland County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L37.1%
2 to 4 pCi/L614.3%
4 pCi/L and above3378.6%
What these figures count

These are the 42 tests reported to CDC for Richland 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

Richland County, Compared

Richland County radon figures, compared

Calculated by Radon411

More than half: 78.6% of the 42 radon tests reported to CDC for Richland County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 1st of 23 Montana counties with 30 or more tests for the same period. That is 33.1 points above the 45.5% pooled from 51 Montana counties.

The median result, 5.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 21.0 pCi/L. The rest split 7.1% under 2 pCi/L and 14.3% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 78.6% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is McKenzie County, ND at 56.1%, the lowest Williams County, ND at 33.8%. Statewide for the same period, Sheridan County reported the highest share (75.7%) and Cascade County the lowest (29.4%).

CDC's ten-year totals for Richland County went from 43 tests (2005 to 2014) to 42 (2008 to 2017), the share going from 76.7% to 78.6%.

Nationally, every county with a figure for the same period pools to 35.7%; Richland County sits 42.9 points above it.

Richland County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Richland County
Richland County4278.6%5.9 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled−33.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−42.9 points
Sheridan Countyhighest in the state7075.7%6.5 pCi/L−2.9 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−49.2 points
Roosevelt County, MTborders it1693.8%8.7 pCi/L+15.2 points
McKenzie County, NDborders it4156.1%4.8 pCi/L−22.5 points
Wibaux County, MTborders it450.0%3.0 pCi/L−28.6 points
Dawson County, MTborders it5947.5%3.5 pCi/L−31.1 points
Williams County, NDborders it20433.8%2.9 pCi/L−44.8 points
McCone County, MTborders it10.0%1.5 pCi/L−78.6 points
Where Richland County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultRichland County testsRichland County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L37.1%29.2%39.6%−22.1 points
2 to 4 pCi/L614.3%25.2%24.7%−10.9 points
4 pCi/L and above3378.6%45.5%35.7%+33.1 points
Richland 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
Richland County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20174278.6%5.9 pCi/L21.0 pCi/L45.5%+3.0 points
2007 to 20164175.6%5.4 pCi/L21.0 pCi/L46.6%+0.6 points
2006 to 20154075.0%5.6 pCi/L21.0 pCi/L47.4%−1.7 points
2005 to 20144376.7%6.3 pCi/L21.0 pCi/L48.0%First on file

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

Richland County, Geology

The ground under Richland County

Predicted

USGS's geologic map puts all of Richland County's mapped land in one class: high radon potential. The map puts 88.1% of Richland County in the area it calls Great Plains (Glaciated) and 11.9% in Great Plains. USGS gives the first a radon index of 13 and the second 12, both in the high band (12 to 17).

USGS's geologic areas under Richland County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Great Plains (Glaciated)Glacial deposits derived from Cretaceous shales containing higher than average amounts of uranium.High1388.1%
Great PlainsTertiary sandstone, siltstone, shale, coal.High1211.9%

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

Richland County beside the ground around it

Richland County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 6 counties that border it, none has as large a share of high-potential ground; McKenzie County, ND comes nearest at 100%.

Share of land by USGS radon potential: Richland County, the 6 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Richland CountyZone 1NoneNone100%
Dawson CountyZone 1None13.0%87.0%
Roosevelt CountyZone 1NoneNone100%
McCone CountyZone 1NoneNone100%
Wibaux CountyZone 1None18.7%81.3%
McKenzie County, NDZone 1NoneNone100%
Williams County, NDZone 1NoneNone100%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Local help

Richland County, Local resources

Radon testing and mitigation in Richland 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

Richland County, Questions

Questions about radon in Richland County

Are radon levels high in Richland County?

Over the 2008 to 2017 laboratory totals, 78.6% of the radon tests reported to CDC for Richland County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.9 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 45.5%.

Which counties border Richland County?

Richland County borders 6 counties: Dawson County, MT, Roosevelt County, MT, McCone County, MT, Wibaux County, MT, McKenzie County, ND and Williams County, ND.

Products

Richland County, Products

Testing a home in Richland County

In Richland County, 78.6% of 42 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 Richland 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

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

Explore

Richland County, Bordering counties

Counties bordering Richland County

Calculated by Radon411

Richland County, Cities and towns

Cities and towns in Richland County

About 11,377 people live in Richland County by the Census Bureau's estimate for July 1, 2025, 150 fewer than in 2020 (−1.3%). Spread over its land, that is 5.5 people to the square mile. Sidney alone is home to 6,217 of them, 54.6% of the total. Together its 2 incorporated places hold 62.4% of those residents; the other 37.6% live outside any of them. Reported testing is thin here: 42 tests over 2008 to 2017, or 3.7 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.6.

From Sidney to Fairview, CDC publishes no figure by town: each reads Richland County's.

The cities and towns in Richland County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Sidney6,217−2.2%54.6%
Fairview882−1.9%7.8%

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).

Richland County, Homes

Homes in Richland County

Of Richland County's 5,590 homes, 63% are detached houses, against 69% across Montana; 18% are mobile homes. Half of its homes were built before 1981, close to Montana's 1980: 25% date from before 1960 and 30% from 2000 or later. 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 Richland County, Montana, 2019 to 2023
HomesRichland CountyMontana
Housing units5,590522,939
Detached houses63%69%
In buildings of 5 or more12%9%
Mobile homes18%10%
Built before 196025%26%
Built since 200030%27%
Middle year built19811980
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.