Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
Locations and reports
Radon Levels in Snohomish County, Washington
EPA puts Snohomish County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 1.0% of 102 (2020) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
1.0%
18.0 pts below WA
- Snohomish
- 1.0%
- Washington
- 19.0%
102 tests, 2020
Median result
0.2pCi/L
Below action level
- Snohomish
- 0.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2020
Tests reported
102
5th of 10 by tests
- Snohomish
- 102
- Spokane
- 721
Reported to CDC before any fix, 2020
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Rank in Washington
9 of 10
Lowest quarter
- Snohomish
- 1.0%
- Spokane
- 40.6%
By share, of 10 with 30+ tests
Read a result for Snohomish County
Starts at Snohomish County's median, 0.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.2 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Snohomish County's median reported result, 2020.
The data
Snohomish County, At a glance
Snohomish County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Snohomish County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 3.8% |
| 2015 | 0.5% |
| 2016 | 0.7% |
| 2017 | 1.1% |
| 2018 | 0.0% |
| 2019 | 0.0% |
| 2020 | 1.0% |
2020: 1.0%. Across these years the share ran from 0.0% to 3.8%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 102 tests reported to CDC for Snohomish County over 2020, 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: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).
Snohomish County, Compared
Snohomish County radon figures, compared
Calculated by Radon411Only 1 of 102 radon tests reported for Snohomish County in 2020 reached 4 pCi/L (1.0%). The median result, 0.2 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 4.4 pCi/L.
Across 37 Washington counties pooled together, 19.0% of tests reached that level, so Snohomish County runs 18.0 points below its state. Against the national pool of 25.5%, the gap is 24.5 points lower. Its place in the state: 9th of 10 Washington counties with 30 or more tests for the same period.
Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 1.0% share point the same way here. King County, the one bordering county with a figure for the same period, reported 5.0%.
Below the action level, 101 tests (99.0%) came in under 2 pCi/L, against 67.6% statewide, and 0 tests (0.0%) fell between 2 and 4, against 13.3% statewide. Over 7 years of annual figures the share fell 2.8 points, from 3.8% in 2014 to 1.0% in 2020; its peak was 3.8% in 2014. USGS geology rates 100% of the county's land low radon potential.
The busiest year on file was 2015, with 185 tests reported; the quietest, 2020, had 102.
Snohomish CountyWashington, pooled
1.0% % of tests19.0% % of tests
| Year | Tests | Snohomish County, at or above 4 pCi/L | Washington, pooled |
|---|---|---|---|
| 2014 | 130 | 3.8% | 15.0% |
| 2015 | 185 | 0.5% | 17.4% |
| 2016 | 141 | 0.7% | 16.6% |
| 2017 | 185 | 1.1% | 19.1% |
| 2018 | 145 | 0.0% | 16.1% |
| 2019 | 145 | 0.0% | 20.9% |
| 2020 | 102 | 1.0% | 19.0% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Snohomish County, Geology
The ground under Snohomish County
PredictedUSGS's geologic map puts all of Snohomish County's mapped land in one class: low radon potential. The map puts 70.8% of Snohomish County in the area it calls Cascade Mountains and 28.9% in Puget Lowlands. USGS gives both a radon index of 6, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Cascade Mountains | Northern 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. | Low | 6 | 70.8% |
| Puget Lowlands | Continental and marine sediments overlain by sandy and silty glacial deposits. | Low | 6 | 28.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Snohomish County beside the ground around it
Across Washington 13.7% of the land is rated high; none of Snohomish County's is. Of the 4 counties that border it, 1 has more moderate-potential ground, Chelan County the most at 3.5%.
The map rates the ground, not the air in any home.
Local help
Snohomish County, Local resources
Radon testing and mitigation in Snohomish County
- Radon ProgramRadon Program, run by Washington State Department of Health, offers free or discounted test kits, and answers questions about testing and mitigation in Washington.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
We have a limited supply of free radon test kits.
- Compare kits
- See the Washington directoryNo professionals are listed in Washington yet. The state program can point you to registered testers and mitigators.
What Washington's program says
- Phone
- 360-236-3200
- doh.radon@doh.wa.gov
What it means
Snohomish County, Questions
Questions about radon in Snohomish County
Are radon levels high in Snohomish County?
In 2020, 1.0% of the radon tests reported to CDC for Snohomish County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.2 pCi/L. Of 10 Washington counties with 30 or more tests for the same period, 8 reported a higher share; pooled, the state comes to 19.0%.
Which counties border Snohomish County?
Snohomish County borders 4 counties: Skagit County, Island County, King County and Chelan County.
Products
Snohomish County, Products
Testing a home in Snohomish County
In Snohomish County, 1.0% of 102 tests reported to CDC in 2020 reached 4 pCi/L, against 19.0% pooled across Washington. 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 Snohomish County.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
RM-63Pro rechargeable radon monitor with a touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Snohomish County, Bordering counties
Counties bordering Snohomish County
Calculated by Radon411- Radon levels in Chelan CountyEPA zone 3
15.0%at or above 4 pCi/L
Median 1.7 pCi/L · 20 tests · 14.0 points above Snohomish County
- Radon levels in King CountyEPA zone 3
5.0%at or above 4 pCi/L
Median 0.3 pCi/L · 503 tests · 4.0 points above Snohomish County
- Radon levels in Skagit CountyEPA zone 3
4.8%at or above 4 pCi/L
Median 0.5 pCi/L · 21 tests · 3.8 points above Snohomish County
- Radon levels in Island CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.1 pCi/L · 6 tests · 1.0 points below Snohomish County
Snohomish County, Cities and towns
Cities and towns in Snohomish County
The Census Bureau estimates 870,656 residents in Snohomish County for July 1, 2025, 40,755 more than in 2020 (+4.9%). That works out to 417 people per square mile of land. No town dominates: Everett, the largest, has 113,567 residents, 13.0% of the total. Reported testing is thin here: 102 tests over 2020, or 0.1 for every 1,000 residents (2025 estimate), where Washington as a whole comes to 0.3.
From Everett to Index, CDC publishes no figure by town: each reads Snohomish County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Everett | 113,567 | +2.5% | 13.0% |
| Marysville | 77,686 | +9.5% | 8.9% |
| Bothellextends beyond Snohomish County | 52,199 | +8.4% | Counted whole |
| Edmonds | 42,748 | −0.2% | 4.9% |
| Lynnwood | 42,132 | +9.3% | 4.8% |
| Lake Stevens | 42,091 | +7.7% | 4.8% |
| Mountlake Terrace | 25,430 | +19.5% | 2.9% |
| Arlington | 22,031 | +9.9% | 2.5% |
| Mukilteo | 21,239 | −1.3% | 2.4% |
| Mill Creek | 20,902 | Level | 2.4% |
| Monroe | 20,025 | Level | 2.3% |
| Snohomish | 10,719 | +5.4% | 1.2% |
- Stanwood
- Sultan
- Brier
- Granite Falls
- Gold Bar
- Darrington
- Woodway
- Index
20 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 Snohomish County is counted whole, so it has no share.
Snohomish County, Homes
Homes in Snohomish County
Of Snohomish County's 327,893 homes, 64% are detached houses, against 62% across Washington; 20% are in buildings of five or more homes. Half of its homes were built before 1989, close to Washington's 1984: 12% date from before 1960 and 31% from 2000 or later. 68% 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 | Snohomish County | Washington |
|---|---|---|
| Housing units | 327,893 | 3,262,667 |
| Detached houses | 64% | 62% |
| In buildings of 5 or more | 20% | 22% |
| Mobile homes | 5% | 6% |
| Built before 1960 | 12% | 21% |
| Built since 2000 | 31% | 28% |
| Middle year built | 1989 | 1984 |
| Owner-occupied | 68% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.