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Radon Levels in Idaho County, Idaho

EPA puts Idaho County in Zone 1, its highest radon zone, and high results are common there: 40.0% of the 90 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

    40.0%

    1.5 pts below ID

    Idaho
    40.0%
    Idaho
    41.5%

    90 tests, 2008 to 2017

  • Median result

    2.9pCi/L

    Below action level

    Idaho
    2.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    90

    21st of 37 by tests

    Idaho
    90
    Ada
    3,030

    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 Idaho

    18 of 37

    Middle half

    Idaho
    40.0%
    Bear Lake
    78.1%

    By share, of 37 with 30+ tests

Read a result for Idaho County

Starts at Idaho County's median, 2.9 pCi/L

2.9pCi/L

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

EPA’s reading of 2.9 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. Idaho County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Idaho County, At a glance

Idaho County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Idaho 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 79% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Idaho County, 2008 to 2017, laboratory

Reported results by concentration band, Idaho County, 2008 to 2017, laboratory
Under 2 pCi/L: 43%2 to 4 pCi/L: 17%4 pCi/L and above: 40%

Of 90 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Idaho County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L3943.3%
2 to 4 pCi/L1516.7%
4 pCi/L and above3640.0%
What these figures count

These are the 90 tests reported to CDC for Idaho 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

Idaho County, Compared

Idaho County radon figures, compared

Calculated by Radon411

In Idaho County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (36 of 90) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 4.3 points higher. Across 44 Idaho counties pooled together, 41.5% of tests reached that level, so Idaho County runs 1.5 points below its state.

Of 7 neighbours with a figure, 4 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 22.1% (Nez Perce County) to 65.2% (Lemhi County). By share, Idaho County is 18th of 37 Idaho counties with 30 or more tests for the same period.

Half the tests came in under 2.9 pCi/L and half over it; the single highest reached 54.9 pCi/L. Below the action level, 39 tests (43.3%) came in under 2 pCi/L, against 31.5% statewide, and 15 tests (16.7%) fell between 2 and 4, against 26.9% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 40.0% share point the same way here. USGS geology rates 79% of the county's land high radon potential.

CDC's ten-year totals for Idaho County went from 69 tests (2005 to 2014) to 90 (2008 to 2017), the share going from 46.4% to 40.0%.

Idaho County against Idaho, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Idaho County
Idaho County9040.0%2.9 pCi/LThis county
Idaho, pooled44 counties, pooled12,96141.5%Not pooled+1.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−4.3 points
Bear Lake Countyhighest in the state3278.1%7.8 pCi/L+38.1 points
Payette Countylowest in the state614.9%1.5 pCi/L−35.1 points
Lemhi County, IDborders it11265.2%5.2 pCi/L+25.2 points
Adams County, IDborders it3151.6%4.0 pCi/L+11.6 points
Lewis County, IDborders it650.0%3.8 pCi/L+10.0 points
Ravalli County, MTborders it1,09044.6%3.5 pCi/L+4.6 points
Missoula County, MTborders it2,61344.6%3.4 pCi/L+4.6 points
Clearwater County, IDborders it3330.3%1.8 pCi/L−9.7 points
Valley County, IDborders it12827.3%2.3 pCi/L−12.7 points
Wallowa County, ORborders it1526.7%1.1 pCi/L−13.3 points
Nez Perce County, IDborders it14922.1%2.3 pCi/L−17.9 points
Where Idaho County's reported results fell, 2008 to 2017, laboratory, beside Idaho and the United States
ResultIdaho County testsIdaho County shareIdaho shareU.S. shareAgainst Idaho
Under 2 pCi/L3943.3%31.5%39.6%+11.8 points
2 to 4 pCi/L1516.7%26.9%24.7%−10.2 points
4 pCi/L and above3640.0%41.5%35.7%−1.5 points
Idaho 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
Fremont County13 of 3710149.5%3.9 pCi/L
Elmore County14 of 3715848.1%3.8 pCi/L
Caribou County15 of 375743.9%3.4 pCi/L
Bannock County16 of 3773241.9%3.2 pCi/L
Bonneville County17 of 371,11740.1%3.4 pCi/L
Idaho County18 of 379040.0%2.9 pCi/L
Franklin County19 of 377534.7%3.1 pCi/L
Bonner County20 of 3732133.0%2.3 pCi/L
Clearwater County21 of 373330.3%1.8 pCi/L
Gooding County22 of 376728.4%2.4 pCi/L
Valley County23 of 3712827.3%2.3 pCi/L
Idaho County ten-year laboratory totals, against Idaho's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIdaho, pooledChange from the row before
2008 to 20179040.0%2.9 pCi/L54.9 pCi/L41.5%−3.8 points
2007 to 20168043.8%3.3 pCi/L54.9 pCi/L40.8%−2.7 points
2006 to 20157146.5%3.1 pCi/L54.9 pCi/L41.3%+0.1 points
2005 to 20146946.4%3.1 pCi/L54.9 pCi/L41.1%First on file

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

Idaho County, Geology

The ground under Idaho County

Predicted

Most of the ground under Idaho County is one class on USGS's geologic map: 79.3% of its land is high radon potential, with 0.1% moderate and 20.7% low. The map puts 79.2% of Idaho County in the area it calls Northern Rocky Mountain Province and 20.7% in Seven Devils and Tri-State Uplands. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 8, in the low band (5 to 8).

USGS's geologic areas under Idaho County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky Mountain ProvinceDiorite and granite of the Idaho batholith.High1279.2%
Seven Devils and Tri-State UplandsColumbia River basalt flows.Low820.7%

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

Idaho County beside the ground around it

Idaho County has more high-potential ground than Idaho as a whole: 79.3% of its land against 50.7%. Of the 9 counties that border it, 5 have more high-potential ground, Missoula County, MT the most at 100%.

Share of land by USGS radon potential: Idaho County, the 9 counties bordering it and Idaho
AreaEPA zoneLow potentialModerate potentialHigh potential
Idaho CountyZone 120.7%0.1%79.3%
Lewis CountyZone 3100%NoneNone
Clearwater CountyZone 118.8%None81.2%
Nez Perce CountyZone 399.5%0.5%None
Ravalli County, MTZone 1NoneNone100%
Wallowa County, ORZone 3None100%None
Valley CountyZone 1NoneNone100%
Adams CountyZone 384.7%0.3%15.1%
Lemhi CountyZone 1NoneNone100%
Missoula County, MTZone 1NoneNone100%
Idaho44 counties, pooled by land areaVaries8.0%41.3%50.7%

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

Local help

Idaho County, Local resources

Radon testing and mitigation in Idaho County

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

What it means

Idaho County, Questions

Questions about radon in Idaho County

Are radon levels high in Idaho County?

Over the 2008 to 2017 laboratory totals, 40.0% of the radon tests reported to CDC for Idaho County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.9 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 17 reported a higher share; pooled, the state comes to 41.5%.

Which counties border Idaho County?

Idaho County borders 9 counties: Lewis County, ID, Clearwater County, ID, Nez Perce County, ID, Ravalli County, MT, Wallowa County, OR, Valley County, ID, Adams County, ID, Lemhi County, ID and Missoula County, MT.

Products

Idaho County, Products

Testing a home in Idaho County

In Idaho County, 40.0% of 90 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. In Zone 1 the year-round level in Idaho 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

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

Explore

Idaho County, Bordering counties

Counties bordering Idaho County

Calculated by Radon411

Idaho County, Cities and towns

Cities and towns in Idaho County

Idaho County is growing: the Census Bureau puts it at 17,874 residents on July 1, 2025, up 7.7% from 16,592 in 2020. Spread over its land, that is 2.1 people to the square mile. Its largest town, Grangeville, has 3,621 residents, 20.3% of the total. CDC's 90 reported tests for 2008 to 2017 work out to 5.0 per 1,000 residents (2025 estimate), close to Idaho's 6.4.

From Grangeville to White Bird, CDC publishes no figure by town: each reads Idaho County's.

The cities and towns in Idaho County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Grangeville3,621+8.9%20.3%
Kamiahextends beyond Idaho County1,134+1.5%Counted whole
Cottonwood921+12.3%5.2%
Kooskia550+7.4%3.1%
Riggins396+7.3%2.2%
Stites184+8.2%1.0%
Ferdinand141+7.6%0.8%
White Bird83+7.8%0.5%

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

Idaho County, Homes

Homes in Idaho County

Idaho County is a place of houses on their own lots: 79% of its 8,881 homes are detached single-family houses, against 74% across Idaho. The homes are older than Idaho's as a whole: half were built before 1979 (1990 for Idaho), and 22% date from before 1960. Owners live in 80% of the occupied homes (Idaho: 72%), so for most households a test and a fix are their own to order.

Homes in Idaho County, Idaho, 2019 to 2023
HomesIdaho CountyIdaho
Housing units8,881776,683
Detached houses79%74%
In buildings of 5 or more2%9%
Mobile homes15%7%
Built before 196022%18%
Built since 200020%35%
Middle year built19791990
Owner-occupied80%72%

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