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 Jefferson County, Washington
EPA puts Jefferson County in Zone 3, its lowest radon zone, and only 7 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
Nearest county
4.9%
Kitsap County, 44 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
- Jefferson
- 0.0%
- Washington
- 52.7%
Share of land USGS rates moderate or high potential
Tests reported
24
Too few for a share
- Jefferson
- 24
- Needed
- 30
2006 to 2015, laboratory
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 Jefferson 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
Jefferson County, At a glance
Jefferson County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 99% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Jefferson County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 0.0% |
| 2015 | 0.0% |
| 2016 | 4.8% |
| 2017 | 0.0% |
| 2019 | 28.6% |
| 2020 | 14.3% |
2020: 14.3%. Across these years the share ran from 0.0% to 28.6%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 7 tests were reported to CDC for Jefferson 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).
Jefferson County, Compared
Jefferson County radon figures, compared
Calculated by Radon411CDC's largest figure for Jefferson County rests on 24 tests over the 2006 to 2015 laboratory totals, 2 of them at or above 4 pCi/L, so each test moves its share by 4.2 points and no rank or comparison is drawn from it. Results reached as high as 57.2 pCi/L, with a middle value of 0.8 pCi/L.
The nearest counties with a figure are Kitsap County (44 miles away) at 4.9%, Thurston County (67 miles away) at 10.1% and King County (85 miles away) at 2.6%. 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 Jefferson County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 99% of the county's land low radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Jefferson County, Geology
The ground under Jefferson County
PredictedUSGS's geologic map puts all of Jefferson County's mapped land in one class: low radon potential. The map puts 94.4% of Jefferson County in the area it calls Coastal Mountains and 4.3% 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 |
|---|---|---|---|---|
| Coastal Mountains | Cretaceous and Tertiary continental and marine sedimentary rocks and pre-Miocene volcanic rocks. | Low | 6 | 94.4% |
| Puget Lowlands | Continental and marine sediments overlain by sandy and silty glacial deposits. | Low | 6 | 4.3% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Jefferson County beside the ground around it
Across Washington 13.7% of the land is rated high; none of Jefferson County's is. None of the 3 counties that border it has any moderate-potential ground either.
The map rates the ground, not the air in any home.
Local help
Jefferson County, Local resources
Radon testing and mitigation in Jefferson 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
Jefferson County, Questions
Questions about radon in Jefferson County
Are radon levels high in Jefferson County?
In 2020, 14.3% of the radon tests reported to CDC for Jefferson County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.6 pCi/L. Of the 8 nearest counties with a figure, within 116 miles, the share of tests at or above 4 pCi/L runs from 2.3% to 11.3%.
Which counties border Jefferson County?
Jefferson County borders 3 counties: Clallam County, Mason County and Grays Harbor County.
Products
Jefferson County, Products
Testing a home in Jefferson County
No CDC figure names Jefferson County; the nearest county with one, Kitsap County (44 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 Jefferson 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
EcoQube Flex battery digital radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Alarm
- Screen, app
Method: Ion chamber
First reading: Within 15 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Jefferson County, Bordering counties
Counties bordering Jefferson 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 Clallam CountyEPA zone 3
11.8%at or above 4 pCi/L
Median 0.1 pCi/L · 17 tests
- Radon levels in Mason CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.7 pCi/L · 14 tests
Jefferson County, Cities and towns
Cities and towns in Jefferson County
The Census Bureau estimates 33,970 residents in Jefferson County for July 1, 2025, 906 more than in 2020 (+2.7%). That works out to 19 people per square mile of land. Port Townsend, its one incorporated place, has 10,678 residents, 31.4% of the total. CDC's 24 reported tests for 2006 to 2015 work out to 0.7 per 1,000 residents (2025 estimate), close to Washington's 0.9.
Port Townsend is the one incorporated place here; CDC publishes no figure by town, so it reads Jefferson County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Port Townsend | 10,678 | +4.9% | 31.4% |
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).
Jefferson County, Homes
Homes in Jefferson County
Jefferson County is a place of houses on their own lots: 77% of its 19,359 homes are detached single-family houses, against 62% across Washington. Half of its homes were built before 1987, close to Washington's 1984: 15% date from before 1960 and 26% from 2000 or later. Owners live in 80% of the occupied homes (Washington: 64%), so for most households a test and a fix are their own to order.
| Homes | Jefferson County | Washington |
|---|---|---|
| Housing units | 19,359 | 3,262,667 |
| Detached houses | 77% | 62% |
| In buildings of 5 or more | 5% | 22% |
| Mobile homes | 12% | 6% |
| Built before 1960 | 15% | 21% |
| Built since 2000 | 26% | 28% |
| Middle year built | 1987 | 1984 |
| Owner-occupied | 80% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.