Test results in King County
| Result | Share | EPA guidance |
|---|---|---|
| Below 2 pCi/L | 89% | Below EPA's levels |
| 2 to 4 pCi/L | 7% | Consider fixing |
| 4 pCi/L or more | 4% | EPA recommends fixing |
What the data shows
- Higher share of high results than 4 of 39 Washington counties.
- Below the Washington rate of 19%.
- Higher than 2 of 6 neighbouring counties.
- 11% of results at or above 2 pCi/L.
- 11.9 tests per 1,000 homes (Washington: 19.6).
How King County compares
Data table
| Area | Tests ≥ 4 pCi/L | Tests |
|---|---|---|
| Kittitas County | 18% | 209 |
| Chelan County | 16% | 372 |
| Pierce County | 9% | 7,910 |
| Yakima County | 6% | 463 |
| King County | 4% | 11,972 |
| Snohomish County | 2% | 2,799 |
| Kitsap County | 1% | 1,244 |
| Washington (39 counties) | 19% | 64,932 |
Same source as King County.
What it means for your home
About 1 in 26 results in King County were at or above 4 pCi/L, where the EPA recommends a fix. Only a test shows your own home's level.
Levels in pCi/L from the EPA. The WHO reference level is 100 Bq/m³, about 2.7 pCi/L.
Test your home
Start with a short-term test (2–90 days) and confirm a result of 4 pCi/L or more with a second test. EPA guide
Sponsored: we earn a commission on purchases through these links. We haven't tested Airthings monitors yet.
Prefer a digital monitor? See Airthings radon monitors, or enter code radonbycounty-10OFF at their discount store for 10% off.
Fixing high radon
No local job records yet. National range: $800–$2,500, average $1,200 (EPA, 2003). Cost guide →
Washington doesn't license radon mitigators; look for NRPP or NRSB certification. Source
Buying or selling here
Washington's seller disclosure statement asks whether the seller knows of substances that may be environmental concerns, including radon gas (RCW 64.06.020). Source
Checked against the official text on 2026-11-03. Not legal advice.
About this data
Source: Radon test results by county (Washington Tracking Network) (Washington State Department of Health). Period: 2000–2025. Tests: 11,972. Read the methodology →
These are voluntary and real-estate tests, not a random sample of homes, so they describe tested homes rather than every home.
About this page
Published by Ray Roman, editor of Radon by County. Figures are loaded from the cited source and spot-checked against it. Editorial policy · About us