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Radon Levels in Twin Falls County, Idaho

EPA puts Twin Falls County in Zone 2, its middle radon zone, and 24.1% of its 369 reported radon tests (2008 to 2017, laboratory totals) were 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

    24.1%

    17.4 pts below ID

    Twin Falls
    24.1%
    Idaho
    41.5%

    369 tests, 2008 to 2017

  • Median result

    2.4pCi/L

    Below action level

    Twin Falls
    2.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    369

    8th of 37 by tests

    Twin Falls
    369
    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

    27 of 37

    Middle half

    Twin Falls
    24.1%
    Bear Lake
    78.1%

    By share, of 37 with 30+ tests

Read a result for Twin Falls County

Starts at Twin Falls County's median, 2.4 pCi/L

2.4pCi/L

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

EPA’s reading of 2.4 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. Twin Falls County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Twin Falls County, At a glance

Twin Falls County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Twin Falls 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 Twin Falls County, 2008 to 2017, laboratory

Reported results by concentration band, Twin Falls County, 2008 to 2017, laboratory
Under 2 pCi/L: 41%2 to 4 pCi/L: 35%4 pCi/L and above: 24%

Of 369 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Twin Falls County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L15040.7%
2 to 4 pCi/L13035.2%
4 pCi/L and above8924.1%
What these figures count

These are the 369 tests reported to CDC for Twin Falls 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

Twin Falls County, Compared

Twin Falls County radon figures, compared

Calculated by Radon411

Twin Falls County's 369 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.4 pCi/L and a maximum of 19.5 pCi/L, and 24.1% reached 4 pCi/L. Idaho as a whole (44 Idaho counties, pooled) comes to 41.5%: 17.4 points higher than here.

Among its state's counties it ranks 27th of 37 Idaho counties with 30 or more tests for the same period. Statewide for the same period, Bear Lake County reported the highest share (78.1%) and Payette County the lowest (4.9%).

Below the action level, 150 tests (40.7%) came in under 2 pCi/L, against 31.5% statewide, and 130 tests (35.2%) fell between 2 and 4, against 26.9% statewide. CDC's ten-year totals for Twin Falls County went from 307 tests (2005 to 2014) to 369 (2008 to 2017), the share going from 24.8% to 24.1%.

EPA's 1993 zone map puts Twin Falls County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.

Next door, the shares run from 16.9% in Jerome County to 59.5% in Cassia County, with Owyhee County and Jerome County below Twin Falls County.

Twin Falls County against Idaho, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Twin Falls County
Twin Falls County36924.1%2.4 pCi/LThis county
Idaho, pooled44 counties, pooled12,96141.5%Not pooled+17.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+11.6 points
Bear Lake Countyhighest in the state3278.1%7.8 pCi/L+54.0 points
Payette Countylowest in the state614.9%1.5 pCi/L−19.2 points
Cassia County, IDborders it12159.5%5.4 pCi/L+35.4 points
Elmore County, IDborders it15848.1%3.8 pCi/L+24.0 points
Elko County, NVborders it15940.3%3.1 pCi/L+16.2 points
Gooding County, IDborders it6728.4%2.4 pCi/L+4.3 points
Owyhee County, IDborders it3023.3%2.1 pCi/L−0.8 points
Jerome County, IDborders it6516.9%1.9 pCi/L−7.2 points
Where Twin Falls County's reported results fell, 2008 to 2017, laboratory, beside Idaho and the United States
ResultTwin Falls County testsTwin Falls County shareIdaho shareU.S. shareAgainst Idaho
Under 2 pCi/L15040.7%31.5%39.6%+9.2 points
2 to 4 pCi/L13035.2%26.9%24.7%+8.3 points
4 pCi/L and above8924.1%41.5%35.7%−17.4 points
Twin Falls 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
Gooding County22 of 376728.4%2.4 pCi/L
Valley County23 of 3712827.3%2.3 pCi/L
Power County24 of 374126.8%2.5 pCi/L
Latah County25 of 3715026.0%1.7 pCi/L
Ada County26 of 373,03025.2%2.4 pCi/L
Twin Falls County27 of 3736924.1%2.4 pCi/L
Owyhee County28 of 373023.3%2.1 pCi/L
Boise County29 of 375822.4%2.0 pCi/L
Nez Perce County30 of 3714922.1%2.3 pCi/L
Washington County31 of 376720.9%2.1 pCi/L
Gem County32 of 379920.2%1.9 pCi/L
Twin Falls County ten-year laboratory totals, against Idaho's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIdaho, pooledChange from the row before
2008 to 201736924.1%2.4 pCi/L19.5 pCi/L41.5%−0.2 points
2007 to 201630424.3%2.3 pCi/L19.5 pCi/L40.8%−0.5 points
2006 to 201530724.8%2.3 pCi/L38.9 pCi/L41.3%Level
2005 to 201430724.8%2.3 pCi/L38.9 pCi/L41.1%First on file

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

Twin Falls County, Geology

The ground under Twin Falls County

Predicted

USGS's geologic map puts all of Twin Falls County's mapped land in one class: moderate radon potential. The map puts 91.3% of Twin Falls County in the area it calls Owyhee Upland and 8.7% in Eastern Snake river plain and Malheur-Boise-King Section. USGS gives the first a radon index of 9 and the second 10, both in the moderate band (9 to 11).

USGS's geologic areas under Twin Falls County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Owyhee UplandTertiary and Quaternary basalt, andesite, and rhyolite.Moderate991.3%
Eastern Snake river plain and Malheur-Boise-King SectionBasalt flows.Moderate108.7%

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

Twin Falls County beside the ground around it

Across Idaho 50.7% of the land is rated high; none of Twin Falls County's is. Of the 6 counties that border it, 3 have more high-potential ground, Elmore County the most at 65.1%.

Share of land by USGS radon potential: Twin Falls County, the 6 counties bordering it and Idaho
AreaEPA zoneLow potentialModerate potentialHigh potential
Twin Falls CountyZone 2None100%None
Jerome CountyZone 2None100%None
Gooding CountyZone 1None46.2%53.8%
Cassia CountyZone 2None100%None
Elmore CountyZone 1None34.9%65.1%
Elko County, NVZone 2None88.5%11.5%
Owyhee CountyZone 2None100%None
Idaho44 counties, pooled by land areaVaries8.0%41.3%50.7%

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

Local help

Twin Falls County, Local resources

Radon testing and mitigation in Twin Falls County

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

What it means

Twin Falls County, Questions

Questions about radon in Twin Falls County

Are radon levels high in Twin Falls County?

Over the 2008 to 2017 laboratory totals, 24.1% of the radon tests reported to CDC for Twin Falls County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.4 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 26 reported a higher share; pooled, the state comes to 41.5%.

Which counties border Twin Falls County?

Twin Falls County borders 6 counties: Jerome County, ID, Gooding County, ID, Cassia County, ID, Elmore County, ID, Elko County, NV and Owyhee County, ID.

Products

Twin Falls County, Products

Testing a home in Twin Falls County

In Twin Falls County, 24.1% of 369 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 Twin Falls County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Twin Falls County homes, compared

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Twin Falls County, Bordering counties

Counties bordering Twin Falls County

Calculated by Radon411

Twin Falls County, Cities and towns

Cities and towns in Twin Falls County

Twin Falls County is growing: the Census Bureau puts it at 97,539 residents on July 1, 2025, up 7.9% from 90,365 in 2020. That works out to 51 people per square mile of land. Twin Falls alone is home to 56,216 of them, 57.6% of the total. Together its 8 incorporated places hold 73.4% of those residents; the other 26.6% live outside any of them. Reported testing is thin here: 369 tests over 2008 to 2017, or 3.8 for every 1,000 residents (2025 estimate), where Idaho as a whole comes to 6.4.

From Twin Falls to Murtaugh, CDC publishes no figure by town: each reads Twin Falls County's.

The cities and towns in Twin Falls County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Twin Falls56,216+7.9%57.6%
Kimberly5,798+24.7%5.9%
Buhl4,801+5.1%4.9%
Filer3,026+8.7%3.1%
Hansen1,109+1.6%1.1%
Hollister265+9.1%0.3%
Castleford230+7.0%0.2%
Murtaugh124+6.9%0.1%

8 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).

Twin Falls County, Homes

Homes in Twin Falls County

Of Twin Falls County's 35,749 homes, 75% are detached houses, against 74% across Idaho; 7% are mobile homes. The homes are older than Idaho's as a whole: half were built before 1980 (1990 for Idaho), and 26% 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 Twin Falls County, Idaho, 2019 to 2023
HomesTwin Falls CountyIdaho
Housing units35,749776,683
Detached houses75%74%
In buildings of 5 or more5%9%
Mobile homes7%7%
Built before 196026%18%
Built since 200031%35%
Middle year built19801990
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.