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Radon Levels in Cassia County, Idaho

EPA puts Cassia County in Zone 2, its middle radon zone, and high results are common there: 59.5% of the 121 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

    59.5%

    18.0 pts above ID

    Cassia
    59.5%
    Idaho
    41.5%

    121 tests, 2008 to 2017

  • Median result

    5.4pCi/L

    Action level reached

    Cassia
    5.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    121

    17th of 37 by tests

    Cassia
    121
    Ada
    3,030

    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 Idaho

    8 of 37

    Top quarter

    Cassia
    59.5%
    Bear Lake
    78.1%

    By share, of 37 with 30+ tests

Read a result for Cassia County

Starts at Cassia County's median, 5.4 pCi/L

5.4pCi/L

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

EPA’s reading of 5.4 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. Cassia County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Cassia County, At a glance

Cassia County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Cassia 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 Cassia County, 2008 to 2017, laboratory

Reported results by concentration band, Cassia County, 2008 to 2017, laboratory
Under 2 pCi/L: 17%2 to 4 pCi/L: 24%4 pCi/L and above: 59%

Of 121 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Cassia County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2016.5%
2 to 4 pCi/L2924.0%
4 pCi/L and above7259.5%
What these figures count

These are the 121 tests reported to CDC for Cassia 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

Cassia County, Compared

Cassia County radon figures, compared

Calculated by Radon411

More than half: 59.5% of the 121 radon tests reported to CDC for Cassia County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 8th of 37 Idaho counties with 30 or more tests for the same period. That is 18.0 points above the 41.5% pooled from 44 Idaho counties.

The median result, 5.4 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 41.3 pCi/L. The rest split 16.5% under 2 pCi/L and 24.0% from 2 to 4 (Idaho: 31.5% and 26.9%). The reported tests do not follow EPA's Zone 2 label for Cassia County (predicted average between 2 and 4 pCi/L): 59.5% of them reached 4 pCi/L, fewer than that label suggests.

1 of its 7 bordering counties with figures ran higher, led by Box Elder County, UT at 64.3%; Minidoka County reported 15.3%. Statewide for the same period, Bear Lake County reported the highest share (78.1%) and Payette County the lowest (4.9%).

CDC's ten-year totals for Cassia County went from 63 tests (2005 to 2014) to 121 (2008 to 2017), the share going from 52.4% to 59.5%.

Nationally, every county with a figure for the same period pools to 35.7%; Cassia County sits 23.8 points above it. CDC also counts 6 tests taken after mitigation in Cassia County for the same period: tests in homes where a fix was already in.

Cassia County against Idaho, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Cassia County
Cassia County12159.5%5.4 pCi/LThis county
Idaho, pooled44 counties, pooled12,96141.5%Not pooled−18.0 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−23.8 points
Bear Lake Countyhighest in the state3278.1%7.8 pCi/L+18.6 points
Payette Countylowest in the state614.9%1.5 pCi/L−54.6 points
Oneida County, IDborders it2774.1%6.5 pCi/L+14.6 points
Box Elder County, UTborders it44064.3%5.8 pCi/L+4.8 points
Blaine County, IDborders it35257.7%5.3 pCi/L−1.8 points
Elko County, NVborders it15940.3%3.1 pCi/L−19.2 points
Power County, IDborders it4126.8%2.5 pCi/L−32.7 points
Twin Falls County, IDborders it36924.1%2.4 pCi/L−35.4 points
Jerome County, IDborders it6516.9%1.9 pCi/L−42.6 points
Minidoka County, IDborders it7215.3%1.8 pCi/L−44.2 points
Where Cassia County's reported results fell, 2008 to 2017, laboratory, beside Idaho and the United States
ResultCassia County testsCassia County shareIdaho shareU.S. shareAgainst Idaho
Under 2 pCi/L2016.5%31.5%39.6%−15.0 points
2 to 4 pCi/L2924.0%26.9%24.7%−2.9 points
4 pCi/L and above7259.5%41.5%35.7%+18.0 points
Cassia County ranked among the 37 Idaho counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Jefferson County3 of 3720767.1%5.7 pCi/L
Lemhi County4 of 3711265.2%5.2 pCi/L
Madison County5 of 3731463.7%6.2 pCi/L
Shoshone County6 of 378163.0%5.7 pCi/L
Kootenai County7 of 372,95561.0%6.0 pCi/L
Cassia County8 of 3712159.5%5.4 pCi/L
Blaine County9 of 3735257.7%5.3 pCi/L
Teton County10 of 3747353.3%4.4 pCi/L
Bingham County11 of 3744652.0%4.2 pCi/L
Adams County12 of 373151.6%4.0 pCi/L
Fremont County13 of 3710149.5%3.9 pCi/L
Cassia County ten-year laboratory totals, against Idaho's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIdaho, pooledChange from the row before
2008 to 201712159.5%5.4 pCi/L41.3 pCi/L41.5%−3.0 points
2007 to 20169662.5%5.8 pCi/L26.2 pCi/L40.8%+0.5 points
2006 to 20159262.0%5.6 pCi/L26.2 pCi/L41.3%+9.6 points
2005 to 20146352.4%4.4 pCi/L25.2 pCi/L41.1%First on file

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

Cassia County, Geology

The ground under Cassia County

Predicted

USGS's geologic map puts all of Cassia County's mapped land in one class: moderate radon potential. The map puts 62.7% of Cassia County in the area it calls Basin and Range and 30.6% in Owyhee Upland, with one smaller area beside them. USGS gives the first a radon index of 11 and the second 9, both in the moderate band (9 to 11).

USGS's geologic areas under Cassia County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Basin and RangeCenozoic to Paleozoic sedimentary rocks.Moderate1162.7%
Owyhee UplandTertiary and Quaternary basalt, andesite, and rhyolite.Moderate930.6%
Eastern Snake river plain and Malheur-Boise-King SectionBasalt flows.Moderate106.6%

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

Cassia County beside the ground around it

Across Idaho 50.7% of the land is rated high; none of Cassia County's is. Of the 8 counties that border it, 4 have more high-potential ground, Blaine County the most at 63.2%.

Share of land by USGS radon potential: Cassia County, the 8 counties bordering it and Idaho
AreaEPA zoneLow potentialModerate potentialHigh potential
Cassia CountyZone 2None100%None
Jerome CountyZone 2None100%None
Minidoka CountyZone 2None100%None
Twin Falls CountyZone 2None100%None
Power CountyZone 2None100%None
Oneida CountyZone 2None99.6%0.4%
Blaine CountyZone 1None36.8%63.2%
Box Elder County, UTZone 2None97.4%2.6%
Elko County, NVZone 2None88.5%11.5%
Idaho44 counties, pooled by land areaVaries8.0%41.3%50.7%

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

Local help

Cassia County, Local resources

Radon testing and mitigation in Cassia County

What Idaho's program says
Phone
800-445-8647
Email
radon@dhw.idaho.gov

What it means

Cassia County, Questions

Questions about radon in Cassia County

Are radon levels high in Cassia County?

Over the 2008 to 2017 laboratory totals, 59.5% of the radon tests reported to CDC for Cassia County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.4 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 7 reported a higher share; pooled, the state comes to 41.5%.

Which counties border Cassia County?

Cassia County borders 8 counties: Jerome County, ID, Minidoka County, ID, Twin Falls County, ID, Power County, ID, Oneida County, ID, Blaine County, ID, Box Elder County, UT and Elko County, NV.

Products

Cassia County, Products

Testing a home in Cassia County

In Cassia County, 59.5% of 121 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Cassia County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Cassia County homes, compared

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Cassia County, Bordering counties

Counties bordering Cassia County

Calculated by Radon411

Cassia County, Cities and towns

Cities and towns in Cassia County

Cassia County is growing: the Census Bureau puts it at 26,397 residents on July 1, 2025, up 6.6% from 24,753 in 2020. That works out to 10 people per square mile of land. Burley, the largest place on its list (12,409 residents in all), extends beyond Cassia County, so no share of the total is worked out for it. CDC's 121 reported tests for 2008 to 2017 work out to 4.6 per 1,000 residents (2025 estimate), close to Idaho's 6.4.

From Burley to Malta, CDC publishes no figure by town: each reads Cassia County's.

The cities and towns in Cassia County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Burleyextends beyond Cassia County12,409+5.5%Counted whole
Oakley835+7.1%3.2%
Declo372+9.1%1.4%
Albion267+7.2%1.0%
Malta181+9.0%0.7%

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). A place that extends beyond Cassia County is counted whole, so it has no share.

Cassia County, Homes

Homes in Cassia County

Cassia County is a place of houses on their own lots: 79% of its 8,992 homes are detached single-family houses, against 74% across Idaho. The homes are older than Idaho's as a whole: half were built before 1975 (1990 for Idaho), and 30% date from before 1960. 70% of occupied homes are lived in by their owner (Idaho: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Cassia County, Idaho, 2019 to 2023
HomesCassia CountyIdaho
Housing units8,992776,683
Detached houses79%74%
In buildings of 5 or more4%9%
Mobile homes10%7%
Built before 196030%18%
Built since 200018%35%
Middle year built19751990
Owner-occupied70%72%

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