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Radon Levels in San Juan County, Washington

EPA puts San Juan County in Zone 3, its lowest radon zone, and only 4 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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  • Nearest county

    2.8%

    Skagit County, 57 miles

    Skagit
    2.8%
    Washington
    25.5%

    Share at 4+ pCi/L, 36 tests, 2008 to 2017

  • Washington, pooled

    25.5%

    10.2 pts below U.S.

    Washington
    25.5%
    U.S.
    35.7%

    39 counties added up, 2008 to 2017

  • Tests reported

    15

    Too few for a share

    San Juan
    15
    Needed
    30

    2007 to 2016, laboratory

  • EPA radon zone

    Zone 3

    Lower potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    EPA predicts under 2 pCi/L indoors

Read a result for San Juan County

Starts at EPA's action level

4.0pCi/L

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

EPA’s reading of 4.0 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.

Interpret this readingWhat a fix costs

The data

San Juan County, At a glance

San Juan County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for San Juan County as a whole is an average indoor of less than 2 pCi/L (less than 75 Bq/m³). A low zone clears no address in it: homes above EPA's turn up in all three zones.

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for San Juan County, 2020

Share of reported tests at or above 4 pCi/L, by year, San Juan County
Share of reported tests at or above 4 pCi/L, by year, San Juan County
YearShare of reported tests at or above 4 pCi/L
20140.0%
20150.0%
20160.0%
20170.0%
20180.0%
20190.0%
202025.0%

2020: 25.0%. Across these years the share ran from 0.0% to 25.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 4 tests were reported to CDC for San Juan 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

San Juan County, Compared

San Juan County radon figures, compared

Calculated by Radon411

CDC's largest figure for San Juan County rests on 15 tests over the 2007 to 2016 laboratory totals, 0 of them at or above 4 pCi/L, so each test moves its share by 6.7 points and no rank or comparison is drawn from it. Results reached as high as 2.1 pCi/L, with a middle value of 0.7 pCi/L.

The nearest counties with a figure are Skagit County (57 miles away) at 2.8%, Whatcom County (59 miles away) at 5.4% and Kitsap County (68 miles away) at 4.9%. Pooled across 39 Washington counties, 25.5% of reported tests reached that level; across every county in the country with a figure, 35.7%.

Statewide for the same period, Pend Oreille County reported the highest share (63.2%) and Snohomish County the lowest (2.3%). EPA's 1993 map puts San Juan County in Zone 3, its lowest label: a predicted county average under 2 pCi/L.

Washington, the United States and the counties around San Juan County, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedian
Washington, pooled39 counties, pooled8,20125.5%Not pooled
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled
Pend Oreille Countyhighest in the state3863.2%4.8 pCi/L
Snohomish Countylowest in the state2652.3%0.5 pCi/L
The nearest Washington counties to San Juan County with 30 or more tests, 2008 to 2017, laboratory
CountyDistanceTestsAt or above 4 pCi/LMedian
Skagit County57 mi362.8%0.8 pCi/L
Whatcom County59 mi1115.4%0.9 pCi/L
Kitsap County68 mi824.9%0.7 pCi/L
Snohomish County69 mi2652.3%0.5 pCi/L
King County92 mi1,2672.6%0.7 pCi/L
Thurston County114 mi19810.1%0.7 pCi/L
Pierce County115 mi2264.9%0.7 pCi/L
Chelan County119 mi4814.6%1.8 pCi/L
San Juan County radon tests by year, against Washington's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWashington, pooledChange from the row before
2020425.0%1.2 pCi/L4.6 pCi/L19.0%+25.0 points
201920.0%1.7 pCi/L3.1 pCi/L20.9%Level
201820.0%0.8 pCi/L1.0 pCi/L16.1%Level
201750.0%0.9 pCi/L1.7 pCi/L19.1%Level
201610.0%0.1 pCi/L0.1 pCi/L16.6%Level
201530.0%0.2 pCi/L0.9 pCi/L17.4%Level
201420.0%0.5 pCi/L0.5 pCi/L15.0%First on file

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

Local help

San Juan County, Local resources

Radon testing and mitigation in San Juan County

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

What it means

San Juan County, Questions

Questions about radon in San Juan County

Are radon levels high in San Juan County?

In 2020, 25.0% of the radon tests reported to CDC for San Juan County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.2 pCi/L. Of the 8 nearest counties with a figure, within 119 miles, the share of tests at or above 4 pCi/L runs from 2.3% to 14.6%.

Which counties border San Juan County?

No county is recorded as sharing a land boundary with San Juan County.

Products

San Juan County, Products

Testing a home in San Juan County

No CDC figure names San Juan County; the nearest county with one, Skagit County (57 miles away), reported 2.8% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in San Juan County.

Test kits and monitors3

See every kit and monitor

Best radon monitors for San Juan County homes, compared

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San Juan County, Bordering counties

Counties bordering San Juan County

Calculated by Radon411

No bordering counties on file

San Juan County has no county recorded as sharing a land boundary with it. Island and coastal county equivalents legitimately have none.

San Juan County, Cities and towns

Cities and towns in San Juan County

The Census Bureau estimates 18,577 residents in San Juan County for July 1, 2025, 752 more than in 2020 (+4.2%). That works out to 107 people per square mile of land. Friday Harbor, its one incorporated place, has 2,729 residents, 14.7% of the total. CDC's 15 reported tests for 2007 to 2016 work out to 0.8 per 1,000 residents (2025 estimate), close to Washington's 1.0.

Friday Harbor is the one incorporated place here; CDC publishes no figure by town, so it reads San Juan County's.

Friday Harbor, San Juan County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Friday Harbor2,729+3.7%14.7%

One incorporated place, 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).

San Juan County, Homes

Homes in San Juan County

San Juan County is a place of houses on their own lots: 87% of its 13,951 homes are detached single-family houses, against 62% across Washington. Half of its homes were built before 1988, close to Washington's 1984: 11% date from before 1960 and 28% from 2000 or later. Owners live in 78% of the occupied homes (Washington: 64%), so for most households a test and a fix are their own to order.

Homes in San Juan County, Washington, 2019 to 2023
HomesSan Juan CountyWashington
Housing units13,9513,262,667
Detached houses87%62%
In buildings of 5 or more3%22%
Mobile homes6%6%
Built before 196011%21%
Built since 200028%28%
Middle year built19881984
Owner-occupied78%64%

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