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Radon Levels in Okanogan County, Washington

EPA puts Okanogan County in Zone 1, its highest radon zone, and only 28 radon tests from it are on file with CDC (2020). 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

    25.4%

    8.8 pts above WA

    Okanogan
    25.4%
    Washington
    16.6%

    59 tests, 2016

  • Median result

    1.1pCi/L

    Below action level

    Okanogan
    1.1 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2016

  • Tests reported

    59

    8th of 14 by tests

    Okanogan
    59
    Clark
    1,506

    Reported to CDC before any fix, 2016

  • 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 Washington

    5 of 14

    Middle half

    Okanogan
    25.4%
    Stevens
    42.3%

    By share, of 14 with 30+ tests

Read a result for Okanogan County

Starts at Okanogan County's median, 1.1 pCi/L

1.1pCi/L

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

EPA’s reading of 1.1 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Okanogan County's median reported result, 2016.

Interpret this reading

The data

Okanogan County, At a glance

Okanogan County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Okanogan 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: Low across 61% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Okanogan County, 2020

Share of reported tests at or above 4 pCi/L, by year, Okanogan County
Share of reported tests at or above 4 pCi/L, by year, Okanogan County
YearShare of reported tests at or above 4 pCi/L
201440.0%
201517.4%
201625.4%
201712.5%
201815.8%
201930.0%
202060.7%

2020: 60.7%. Across these years the share ran from 12.5% to 60.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 28 tests were reported to CDC for Okanogan County over 2020, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.

Measured: CDC tracking data. Figure above: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).

How to read these figures

Okanogan County, Compared

Okanogan County radon figures, compared

Calculated by Radon411

Okanogan County's 59 reported tests in 2016 had a middle value of 1.1 pCi/L and a maximum of 42.2 pCi/L, and 25.4% reached 4 pCi/L. Washington as a whole (37 Washington counties, pooled) comes to 16.6%: 8.8 points lower than here.

The newest figure, in 2020, counts only 28 tests (60.7% at or above 4 pCi/L), too few to compare, so this reading uses the 59-test figure.

Among its state's counties it ranks 5th of 14 Washington counties with 30 or more tests for the same period. Statewide for the same period, Stevens County reported the highest share (42.3%) and Snohomish County the lowest (0.7%).

Below the action level, 40 tests (67.8%) came in under 2 pCi/L, against 67.8% statewide, and 4 tests (6.8%) fell between 2 and 4, against 15.5% statewide. The busiest year on file was 2016, with 59 tests reported; the quietest, 2014, had 10.

EPA's 1993 zone map puts Okanogan County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 61% of the county's land low radon potential.

Whatcom County, the one bordering county with a figure for the same period, reported 2.6%. Over 3 years of annual figures the share rose 12.6 points, from 17.4% in 2015 to 30.0% in 2019; its peak was 30.0% in 2019.

Share of reported tests at or above 4 pCi/L by year, Okanogan County against Washington2015 to 2019, years with 30 or more tests: Okanogan County 17.4% to 30.0%, the state's pooled share 20.9% in 2019.
Okanogan CountyWashington, pooled
Share of reported tests at or above 4 pCi/L by year, Okanogan County against Washington: data table
YearTestsOkanogan County, at or above 4 pCi/LWashington, pooled
20154617.4%17.4%
20165925.4%16.6%
20195030.0%20.9%
Okanogan County against Washington, the United States and nearby counties, 2016
AreaTestsAt or above 4 pCi/LMedianDifference from Okanogan County
Okanogan County5925.4%1.1 pCi/LThis county
Washington, pooled37 counties, pooled4,77216.6%Not pooled−8.8 points
United States, pooled886 counties, pooled398,20731.2%Not pooled+5.8 points
Stevens Countyhighest in the state5242.3%3.0 pCi/L+16.9 points
Snohomish Countylowest in the state1410.7%0.2 pCi/L−24.7 points
Ferry County, WAborders it1421.4%1.9 pCi/L−4.0 points
Grant County, WAborders it1915.8%0.7 pCi/L−9.6 points
Whatcom County, WAborders it392.6%0.6 pCi/L−22.8 points
Chelan County, WAborders it160.0%0.9 pCi/L−25.4 points
Skagit County, WAborders it90.0%0.8 pCi/L−25.4 points
Lincoln County, WAborders it10.0%2.8 pCi/L−25.4 points
Douglas County, WAborders it20.0%1.1 pCi/L−25.4 points
Where Okanogan County's reported results fell, 2016, beside Washington and the United States
ResultOkanogan County testsOkanogan County shareWashington shareU.S. shareAgainst Washington
Under 2 pCi/L4067.8%67.8%44.8%Level
2 to 4 pCi/L46.8%15.5%24.0%−8.7 points
4 pCi/L and above1525.4%16.6%31.2%+8.8 points
Okanogan County ranked among the 14 Washington counties with 30 or more tests, by share at or above 4 pCi/L, 2016
CountyRankTestsAt or above 4 pCi/LMedian
Stevens County1 of 145242.3%3.0 pCi/L
Spokane County2 of 1475038.9%2.8 pCi/L
Pend Oreille County3 of 145534.5%2.3 pCi/L
Skamania County4 of 143330.3%2.8 pCi/L
Okanogan County5 of 145925.4%1.1 pCi/L
Benton County6 of 1411124.3%1.8 pCi/L
Clark County7 of 141,50620.0%1.4 pCi/L
Whitman County8 of 143218.8%2.5 pCi/L
Cowlitz County9 of 14619.8%0.7 pCi/L
King County10 of 146194.8%0.6 pCi/L
Pierce County11 of 141,0303.6%0.5 pCi/L
Okanogan County radon tests by year, against Washington's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWashington, pooledChange from the row before
20202860.7%7.9 pCi/L42.5 pCi/L19.0%+30.7 points
20195030.0%1.4 pCi/L54.9 pCi/L20.9%+14.2 points
20181915.8%1.4 pCi/L6.0 pCi/L16.1%+3.3 points
20171612.5%2.6 pCi/L13.5 pCi/L19.1%−12.9 points
20165925.4%1.1 pCi/L42.2 pCi/L16.6%+8.0 points
20154617.4%0.7 pCi/L12.0 pCi/L17.4%−22.6 points
20141040.0%1.2 pCi/L36.4 pCi/L15.0%First on file

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

Okanogan County, Geology

The ground under Okanogan County

Predicted

USGS's geologic map splits Okanogan County: 61.3% of its land is low radon potential and 38.7% high. The map puts 61.3% of Okanogan County in the area it calls Cascade Mountains and 38.7% in Okanogan Highland. USGS gives the first a radon index of 6, in the low band (5 to 8), and the second 16, in the high band (12 to 17).

USGS's geologic areas under Okanogan County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Cascade MountainsNorthern Cascade Mountains are Mesozoic metamorphic rocks intruded by Mesozoic and Tertiary granitic rocks. Southern Cascade Mountains are composed primarily of Tertiary and Holocene volcanic rocks.Low661.3%
Okanogan HighlandGlaciofluvial outwash and granitic material. Outwash is generally uranium-bearing.High1638.7%

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

Okanogan County beside the ground around it

Okanogan County has more high-potential ground than Washington as a whole: 38.7% of its land against 13.7%. Of the 7 counties that border it, 1 has more high-potential ground, Ferry County the most at 99.6%.

Share of land by USGS radon potential: Okanogan County, the 7 counties bordering it and Washington
AreaEPA zoneLow potentialModerate potentialHigh potential
Okanogan CountyZone 161.3%None38.7%
Chelan CountyZone 396.5%3.5%None
Douglas CountyZone 27.3%87.4%5.3%
Ferry CountyZone 1None0.4%99.6%
Grant CountyZone 2None99.5%0.5%
Lincoln CountyZone 2None95.3%4.7%
Skagit CountyZone 398.5%NoneNone
Whatcom CountyZone 398.9%NoneNone
Washington38 counties, pooled by land areaVaries46.4%39.0%13.7%

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

Local help

Okanogan County, Local resources

Radon testing and mitigation in Okanogan County

What Washington's program says
Phone
360-236-3200
Email
doh.radon@doh.wa.gov

What it means

Okanogan County, Questions

Questions about radon in Okanogan County

Are radon levels high in Okanogan County?

In 2020, 60.7% of the radon tests reported to CDC for Okanogan County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 7.9 pCi/L. Of 14 Washington counties with 30 or more tests for the same period, 4 reported a higher share; pooled, the state comes to 16.6%.

Which counties border Okanogan County?

Okanogan County borders 7 counties: Chelan County, Douglas County, Ferry County, Grant County, Lincoln County, Skagit County and Whatcom County.

Products

Okanogan County, Products

Testing a home in Okanogan County

In Okanogan County, 25.4% of 59 tests reported to CDC in 2016 reached 4 pCi/L, against 16.6% pooled across Washington. In Zone 1 the year-round level in Okanogan 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

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

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Okanogan County, Bordering counties

Counties bordering Okanogan County

Calculated by Radon411

Okanogan County, Cities and towns

Cities and towns in Okanogan County

Okanogan County is growing: the Census Bureau puts it at 45,230 residents on July 1, 2025, up 7.3% from 42,143 in 2020. Spread over its land, that is 8.6 people to the square mile. No town dominates: Omak, the largest, has 5,185 residents, 11.5% of the total. Testing is reported here more often than across the state: CDC's 59 reported tests for 2016 come to 1.3 for every 1,000 residents (2025 estimate), against 0.6 for Washington.

From Omak to Nespelem, CDC publishes no figure by town: each reads Okanogan County's.

The 12 largest cities and towns in Okanogan County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Omak5,185+6.7%11.5%
Okanogan2,494+5.1%5.5%
Brewster2,093+5.4%4.6%
Oroville1,935+6.7%4.3%
Coulee Damextends beyond Okanogan County1,241+2.3%Counted whole
Tonasket1,133+3.0%2.5%
Twisp1,126+12.7%2.5%
Pateros654+9.0%1.4%
Winthrop624+23.1%1.4%
Riverside343+4.9%0.8%
Elmer City258+5.7%0.6%
Conconully198+3.7%0.4%
  • Nespelem

13 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Okanogan County is counted whole, so it has no share.

Okanogan County, Homes

Homes in Okanogan County

Of Okanogan County's 22,015 homes, 74% are detached houses, against 62% across Washington; 18% are mobile homes. Half of its homes were built before 1982, close to Washington's 1984: 23% date from before 1960 and 23% from 2000 or later. 72% of occupied homes are lived in by their owner (Washington: 64%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Okanogan County, Washington, 2019 to 2023
HomesOkanogan CountyWashington
Housing units22,0153,262,667
Detached houses74%62%
In buildings of 5 or more4%22%
Mobile homes18%6%
Built before 196023%21%
Built since 200023%28%
Middle year built19821984
Owner-occupied72%64%

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