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Radon Levels in Washington County, Oregon

EPA puts Washington County in Zone 2, its middle radon zone, and most reported tests there come back low, though 11.4% of 396 (2023) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    11.4%

    7.5 pts below OR

    Washington
    11.4%
    Oregon
    18.9%

    396 tests, 2023

  • Median result

    1.3pCi/L

    Below action level

    Washington
    1.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    396

    2nd of 14 by tests

    Washington
    396
    Multnomah
    792

    Reported to CDC before any fix, 2023

  • 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 Oregon

    10 of 14

    Middle half

    Washington
    11.4%
    Hood River
    39.0%

    By share, of 14 with 30+ tests

Read a result for Washington County

Starts at Washington County's median, 1.3 pCi/L

1.3pCi/L

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

EPA’s reading of 1.3 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. Washington County's median reported result, 2023.

Interpret this reading

The data

Washington County, At a glance

Washington County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Washington 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: Low across 52% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washington County, 2023

Share of reported tests at or above 4 pCi/L, by year, Washington County
Share of reported tests at or above 4 pCi/L, by year, Washington County
YearShare of reported tests at or above 4 pCi/L
201410.9%
201516.6%
201611.9%
20177.8%
201815.4%
201913.8%
202015.3%
202115.8%
202218.9%
202311.4%

2023: 11.4%. Across these years the share ran from 7.8% to 18.9%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 396 tests reported to CDC for Washington County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Washington County, Compared

Washington County radon figures, compared

Calculated by Radon411

Washington County reports fewer high tests than Oregon overall. 11.4% of its 396 tests in 2023 were at or above 4 pCi/L. That is 7.5 points below the 18.9% pooled from 28 Oregon counties.

Ordered from highest share down, it comes 10th of 14 Oregon counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 33.4%; Washington County sits 22.0 points below it.

Next door, the shares run from 15.9% in Clackamas County to 27.8% in Multnomah County. Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 11.4% share point the same way here.

Half the tests came in under 1.3 pCi/L and half over it; the single highest reached 30.8 pCi/L. The rest split 65.7% under 2 pCi/L and 23.0% from 2 to 4 (Oregon: 59.5% and 21.6%). Year by year, 2014 opened at 10.9% and 2023 closed at 11.4% (about level), with 2022 the high at 18.9%.

The busiest year on file was 2016, with 936 tests reported; the quietest, 2019, had 269.

Share of reported tests at or above 4 pCi/L by year, Washington County against Oregon2014 to 2023, years with 30 or more tests: Washington County 10.9% to 11.4%, the state's pooled share 18.9% in 2023.
Washington CountyOregon, pooled
Share of reported tests at or above 4 pCi/L by year, Washington County against Oregon: data table
YearTestsWashington County, at or above 4 pCi/LOregon, pooled
201481410.9%25.1%
201578816.6%27.4%
201693611.9%21.5%
20176577.8%19.2%
201851415.4%19.6%
201926913.8%20.2%
202054315.3%16.8%
202153915.8%16.3%
202250718.9%20.2%
202339611.4%18.9%
Washington County against Oregon, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Washington County
Washington County39611.4%1.3 pCi/LThis county
Oregon, pooled28 counties, pooled2,32918.9%Not pooled+7.5 points
United States, pooled642 counties, pooled128,74033.4%Not pooled+22.0 points
Hood River Countyhighest in the state4139.0%2.2 pCi/L+27.6 points
Deschutes Countylowest in the state601.7%0.9 pCi/L−9.7 points
Clatsop County, ORborders it650.0%3.9 pCi/L+38.6 points
Multnomah County, ORborders it79227.8%2.0 pCi/L+16.4 points
Yamhill County, ORborders it3321.2%1.6 pCi/L+9.8 points
Clackamas County, ORborders it32115.9%1.6 pCi/L+4.5 points
Tillamook County, ORborders it119.1%1.5 pCi/L−2.3 points
Columbia County, ORborders it234.3%0.6 pCi/L−7.1 points
Where Washington County's reported results fell, 2023, beside Oregon and the United States
ResultWashington County testsWashington County shareOregon shareU.S. shareAgainst Oregon
Under 2 pCi/L26065.7%59.5%41.4%+6.2 points
2 to 4 pCi/L9123.0%21.6%25.2%+1.4 points
4 pCi/L and above4511.4%18.9%33.4%−7.5 points
Washington County ranked among the 14 Oregon counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
Yamhill County4 of 143321.2%1.6 pCi/L
Jackson County5 of 144916.3%0.7 pCi/L
Marion County6 of 1419416.0%1.4 pCi/L
Clackamas County7 of 1432115.9%1.6 pCi/L
Benton County8 of 143215.6%0.9 pCi/L
Lane County9 of 145815.5%1.0 pCi/L
Washington County10 of 1439611.4%1.3 pCi/L
Polk County11 of 147910.1%1.4 pCi/L
Lincoln County12 of 14368.3%1.1 pCi/L
Linn County13 of 14414.9%0.8 pCi/L
Deschutes County14 of 14601.7%0.9 pCi/L
Washington County radon tests by year, against Oregon's pooled share
YearTestsAt or above 4 pCi/LMedianHighestOregon, pooledChange from the row before
202339611.4%1.3 pCi/L30.8 pCi/L18.9%−7.5 points
202250718.9%1.5 pCi/L21.8 pCi/L20.2%+3.1 points
202153915.8%1.1 pCi/L50.0 pCi/L16.3%+0.5 points
202054315.3%1.4 pCi/L27.6 pCi/L16.8%+1.5 points
201926913.8%1.3 pCi/L21.4 pCi/L20.2%−1.6 points
201851415.4%1.3 pCi/L38.1 pCi/L19.6%+7.6 points
20176577.8%1.1 pCi/L20.8 pCi/L19.2%−4.1 points
201693611.9%1.2 pCi/L105.8 pCi/L21.5%−4.7 points
201578816.6%1.4 pCi/L29.8 pCi/L27.4%+5.7 points
201481410.9%1.0 pCi/L44.2 pCi/L25.1%First on file

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

Washington County, Geology

The ground under Washington County

Predicted

USGS's geologic map splits Washington County: 51.8% of its land is low radon potential and 48.2% moderate. The map puts 51.8% of Washington County in the area it calls Coast Range and 43.0% in Wilamette Valley, with one smaller area beside them. USGS gives the first a radon index of 7, in the low band (5 to 8), and the second 9, in the moderate band (9 to 11).

USGS's geologic areas under Washington County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Coast RangeNorthern Coast Range is marine sedimentary rocks and Tertiary mafic volcanic rocks. Southern Coast Range is Tertiary estuarine and marine sedimentary rocks, feldspathic and micaceous.Low751.8%
Wilamette ValleyGravelly to clayey alluvium with moderately elevated uranium content.Moderate943.0%
Columbia River GorgeRiver and lacustrine delta deposits and volcanic debris flows.Moderate95.2%

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

Washington County beside the ground around it

Oregon as a whole has more moderate-potential ground than Washington County: 62.3% of its land, against 48.2% here. Of the 6 counties that border it, 3 have more moderate-potential ground, Columbia County the most at 91.6%.

Share of land by USGS radon potential: Washington County, the 6 counties bordering it and Oregon
AreaEPA zoneLow potentialModerate potentialHigh potential
Washington CountyZone 251.8%48.2%None
Multnomah CountyZone 25.3%88.3%None
Yamhill CountyZone 252.4%47.6%None
Columbia CountyZone 24.2%91.6%None
Tillamook CountyZone 397.8%NoneNone
Clatsop CountyZone 231.1%63.3%None
Clackamas CountyZone 386.6%13.4%None
Oregon36 counties, pooled by land areaVaries37.5%62.3%None

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

Local help

Washington County, Local resources

Radon testing and mitigation in Washington County

Listed radon businesses with an address in Washington County:

Listed radon professionals by town: Portland, Beaverton, Tigard, Lake Oswego, Wilsonville, Sherwood

What Oregon's program says
Email
Radon.program@dhsoha.state.or.us

What it means

Washington County, Questions

Questions about radon in Washington County

Are radon levels high in Washington County?

In 2023, 11.4% of the radon tests reported to CDC for Washington County, Oregon were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.3 pCi/L. Of 14 Oregon counties with 30 or more tests for the same period, 9 reported a higher share; pooled, the state comes to 18.9%.

Which counties border Washington County?

Washington County borders 6 counties: Multnomah County, Yamhill County, Columbia County, Tillamook County, Clatsop County and Clackamas County.

Products

Washington County, Products

Testing a home in Washington County

In Washington County, 11.4% of 396 tests reported to CDC in 2023 reached 4 pCi/L, against 18.9% pooled across Oregon. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Washington County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Washington County homes, compared

Explore

Washington County, Bordering counties

Counties bordering Washington County

Calculated by Radon411

Washington County, Cities and towns

Cities and towns in Washington County

The Census Bureau estimates 611,708 residents in Washington County for July 1, 2025, 10,704 more than in 2020 (+1.8%). That works out to 845 people per square mile of land. Portland, the largest place on its list (635,109 residents in all), extends beyond Washington County, so no share of the total is worked out for it. CDC's 396 reported tests for 2023 work out to 0.6 per 1,000 residents (2025 estimate), close to Oregon's 0.5.

From Portland to Rivergrove, CDC publishes no figure by town: each reads Washington County's.

The 12 largest cities and towns in Washington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Portlandextends beyond Washington County635,109−2.7%Counted whole
Hillsboro111,126+3.8%18.2%
Beaverton97,842+0.3%16.0%
Tigard57,929+5.3%9.5%
Lake Oswegoextends beyond Washington County39,722−2.8%Counted whole
Tualatinextends beyond Washington County28,139+0.9%Counted whole
Wilsonvilleextends beyond Washington County27,833+4.2%Counted whole
Forest Grove27,252+4.5%4.5%
Sherwood20,535+0.4%3.4%
Cornelius15,520+21.1%2.5%
King City5,044−2.5%0.8%
North Plains3,414−0.8%0.6%
  • Durham
  • Banks
  • Gaston (part)
  • Rivergrove (part)

16 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 Washington County is counted whole, so it has no share.

Washington County, Homes

Homes in Washington County

Of Washington County's 240,409 homes, 58% are detached houses, against 63% across Oregon; 24% are in buildings of five or more homes. Much of Washington County is recent building: 30% of its homes have gone up since 2000 and the middle year built is 1990, against 1980 for Oregon. 61% of occupied homes are lived in by their owner (Oregon: 63%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Washington County, Oregon, 2019 to 2023
HomesWashington CountyOregon
Housing units240,4091,838,631
Detached houses58%63%
In buildings of 5 or more24%17%
Mobile homes2%8%
Built before 196010%23%
Built since 200030%24%
Middle year built19901980
Owner-occupied61%63%

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