Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Mason County, Washington
EPA puts Mason County in Zone 3, its lowest radon zone, and only 3 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
Highest bordering
10.1%
Thurston County
- Thurston
- 10.1%
- Kitsap
- 4.9%
3 of 5 neighbours have 30+ tests, 2008 to 2017
Nearest county
4.9%
Kitsap County, 30 miles
- Kitsap
- 4.9%
- Washington
- 25.5%
Share at 4+ pCi/L, 82 tests, 2008 to 2017
Ground above low
None
52.7 pts below Washington
- Mason
- 0.0%
- Washington
- 52.7%
Share of land USGS rates moderate or high potential
Tests reported
27
Too few for a share
- Mason
- 27
- Needed
- 30
2015
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Read a result for Mason County
Starts at EPA's action level
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
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 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.
The data
Mason County, At a glance
Mason County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 95% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Mason County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 0.0% |
| 2015 | 0.0% |
| 2016 | 0.0% |
| 2017 | 0.0% |
| 2018 | 0.0% |
| 2019 | 0.0% |
| 2020 | 0.0% |
2020: 0.0%. Across these years the share ran from 0.0% to 0.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 3 tests were reported to CDC for Mason 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).
Mason County, Compared
Mason County radon figures, compared
Calculated by Radon411CDC's largest figure for Mason County rests on 27 tests in 2015, 0 of them at or above 4 pCi/L, so each test moves its share by 3.7 points and no rank or comparison is drawn from it. Results reached as high as 3.3 pCi/L, with a middle value of 0.4 pCi/L.
Of the counties bordering it, 3 have a figure over the 2008 to 2017 laboratory totals: Thurston County reported the largest share at or above 4 pCi/L, 10.1%, and Kitsap County the smallest, 4.9%, with Pierce County at 4.9% between. Farther out, King County (66 miles away) at 2.6%, Cowlitz County (83 miles away) at 11.3% and Snohomish County (85 miles away) at 2.3% have figures too. 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 Mason County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 95% of the county's land low radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mason County, Geology
The ground under Mason County
PredictedUSGS's geologic map puts all of Mason County's mapped land in one class: low radon potential. The map puts 43.0% of Mason County in the area it calls Puget Lowlands and 34.6% in Coastal Mountains, with one smaller area beside them. 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 |
|---|---|---|---|---|
| Puget Lowlands | Continental and marine sediments overlain by sandy and silty glacial deposits. | Low | 6 | 43.0% |
| Coastal Mountains | Cretaceous and Tertiary continental and marine sedimentary rocks and pre-Miocene volcanic rocks. | Low | 6 | 34.6% |
| Coastal Hills | Cretaceous and Tertiary continental and marine sedimentary rocks and pre-Miocene volcanic rocks. | Low | 6 | 17.4% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Mason County beside the ground around it
Across Washington 13.7% of the land is rated high; none of Mason County's is. None of the 5 counties that border it has any moderate-potential ground either.
The map rates the ground, not the air in any home.
Local help
Mason County, Local resources
Radon testing and mitigation in Mason 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
Mason County, Questions
Questions about radon in Mason County
Are radon levels high in Mason County?
In 2020, 0.0% of the radon tests reported to CDC for Mason County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.7 pCi/L. Of the counties bordering it, 3 have a figure over the 2008 to 2017 laboratory totals: Thurston County reported the largest share at or above 4 pCi/L, 10.1%, and Kitsap County the smallest, 4.9%, with Pierce County at 4.9% between.
Which counties border Mason County?
Mason County borders 5 counties: Thurston County, Grays Harbor County, Kitsap County, Jefferson County and Pierce County.
Products
Mason County, Products
Testing a home in Mason County
No CDC figure names Mason County; the nearest county with one, Kitsap County (30 miles away), reported 4.9% 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 Mason 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
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Mason County, Bordering counties
Counties bordering Mason County
Calculated by Radon411- Radon levels in Grays Harbor CountyEPA zone 3
36.4%at or above 4 pCi/L
Median 1.4 pCi/L · 11 tests
- Radon levels in Thurston CountyEPA zone 3
10.1%at or above 4 pCi/L
Median 0.7 pCi/L · 198 tests
- Radon levels in Jefferson CountyEPA zone 3
9.1%at or above 4 pCi/L
Median 1.0 pCi/L · 22 tests
- Radon levels in Kitsap CountyEPA zone 3
4.9%at or above 4 pCi/L
Median 0.7 pCi/L · 82 tests
- Radon levels in Pierce CountyEPA zone 3
4.9%at or above 4 pCi/L
Median 0.7 pCi/L · 226 tests
Mason County, Cities and towns
Cities and towns in Mason County
Mason County is growing: the Census Bureau puts it at 71,165 residents on July 1, 2025, up 7.8% from 66,041 in 2020. That works out to 74 people per square mile of land. Shelton, its one incorporated place, has 10,921 residents, 15.3% of the total. CDC's 27 reported tests for 2015 work out to 0.4 per 1,000 residents (2025 estimate), close to Washington's 0.5.
Shelton is the one incorporated place here; CDC publishes no figure by town, so it reads Mason County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Shelton | 10,921 | +4.7% | 15.3% |
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).
Mason County, Homes
Homes in Mason County
Mason County is a place of houses on their own lots: 77% of its 33,751 homes are detached single-family houses, against 62% across Washington. Half of its homes were built before 1988, close to Washington's 1984: 14% date from before 1960 and 26% from 2000 or later. Owners live in 81% of the occupied homes (Washington: 64%), so for most households a test and a fix are their own to order.
| Homes | Mason County | Washington |
|---|---|---|
| Housing units | 33,751 | 3,262,667 |
| Detached houses | 77% | 62% |
| In buildings of 5 or more | 2% | 22% |
| Mobile homes | 18% | 6% |
| Built before 1960 | 14% | 21% |
| Built since 2000 | 26% | 28% |
| Middle year built | 1988 | 1984 |
| Owner-occupied | 81% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.