Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Washington County, Missouri
EPA puts Washington County in Zone 2, its middle radon zone, and only 2 radon tests from it are on file with CDC (2023). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
26.3%
4.3 pts below MO
- Washington
- 26.3%
- Missouri
- 30.6%
38 tests, 2008 to 2017
Median result
1.5pCi/L
Below action level
- Washington
- 1.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
38
63rd of 72 by tests
- Washington
- 38
- St. Louis
- 17,747
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in Missouri
48 of 72
Middle half
- Washington
- 26.3%
- Atchison
- 69.9%
By share, of 72 with 30+ tests
Read a result for Washington County
Starts at Washington County's median, 1.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.5 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. Washington County's median reported result, 2008 to 2017.
The data
Washington County, At a glance
Washington County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Washington County is a
USGS geologic potential: Moderate across 95% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Washington County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 33.3% |
| 2015 | 0.0% |
| 2016 | 25.0% |
| 2017 | 40.0% |
| 2018 | 0.0% |
| 2019 | 50.0% |
| 2020 | 100.0% |
| 2023 | 100.0% |
2023: 100.0%. Across these years the share ran from 0.0% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 2 tests were reported to CDC for Washington County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Washington County, Compared
Washington County radon figures, compared
Calculated by Radon411Washington County's 38 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.5 pCi/L and a maximum of 15.2 pCi/L, and 26.3% reached 4 pCi/L. Missouri as a whole (115 Missouri counties, pooled) comes to 30.6%: 4.3 points higher than here.
The newest figure, in 2023, counts only 2 tests (100.0% at or above 4 pCi/L), too few to compare, so this reading uses the 38-test figure.
Among its state's counties it ranks 48th of 72 Missouri counties with 30 or more tests for the same period. Statewide for the same period, Atchison County reported the highest share (69.9%) and Vernon County the lowest (8.8%).
Below the action level, 21 tests (55.3%) came in under 2 pCi/L, against 41.2% statewide, and 7 tests (18.4%) fell between 2 and 4, against 28.1% statewide. The busiest year on file was 2017, with 5 tests reported; the quietest, 2020, had 1.
EPA's 1993 zone map puts Washington County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 95% of the county's land moderate radon potential.
Next door, the shares run from 14.7% in Crawford County to 41.6% in Jefferson County, with Crawford County below Washington County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Washington County, Geology
The ground under Washington County
PredictedMost of the ground under Washington County is one class on USGS's geologic map: 94.9% of its land is moderate radon potential, with 5.1% high. The map puts 94.9% of Washington County in the area it calls Salem Plateau and 5.1% in St. Francois Mountains. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Salem Plateau | Ordovician dolomite, sandstone, limestone, and shale. | Moderate | 11 | 94.9% |
| St. Francois Mountains | Granitic and volcanic rocks. Some soils have high uranium concentrations. | High | 13 | 5.1% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Washington County beside the ground around it
On high-potential ground Washington County is close to Missouri as a whole: 5.1% of its land against 8.2%. Of the 5 counties that border it, 2 have more high-potential ground, Iron County the most at 85.3%.
The map rates the ground, not the air in any home.
Local help
Washington County, Local resources
Radon testing and mitigation in Washington County
- Missouri Radon ProgramMissouri Radon Program, run by Missouri Department of Health and Senior Services, offers free or discounted test kits, and answers questions about testing and mitigation in Missouri.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Free radon test kits are available for Missouri residents (limit one per household).
- Compare kits
- Professionals in Missouri27 professionals are listed in Missouri.
What Missouri's program says
- Phone
- 573-751-6102
- radon@health.mo.gov
What it means
Washington County, Questions
Questions about radon in Washington County
Are radon levels high in Washington County?
In 2023, 100.0% of the radon tests reported to CDC for Washington County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 10.4 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 47 reported a higher share; pooled, the state comes to 30.6%.
Which counties border Washington County?
Washington County borders 5 counties: St. Francois County, Crawford County, Jefferson County, Franklin County and Iron County.
Products
Washington County, Products
Testing a home in Washington County
In Washington County, 26.3% of 38 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 30.6% pooled across Missouri. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Washington County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Monitor
Wave Radon battery smart radon monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- App only
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Washington County, Bordering counties
Counties bordering Washington County
Calculated by Radon411- Radon levels in Iron CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 3.5 pCi/L · 14 tests · 23.7 points above Washington County
- Radon levels in Jefferson CountyEPA zone 2
41.6%at or above 4 pCi/L
Median 3.1 pCi/L · 2,652 tests · 15.3 points above Washington County
- Radon levels in St. Francois CountyEPA zone 2
41.1%at or above 4 pCi/L
Median 2.9 pCi/L · 146 tests · 14.8 points above Washington County
- Radon levels in Franklin CountyEPA zone 2
33.2%at or above 4 pCi/L
Median 2.6 pCi/L · 753 tests · 6.9 points above Washington County
- Radon levels in Crawford CountyEPA zone 2
14.7%at or above 4 pCi/L
Median 1.5 pCi/L · 34 tests · 11.6 points below Washington County
Washington County, Cities and towns
Cities and towns in Washington County
The Census Bureau estimates 23,810 residents in Washington County for July 1, 2025, 378 more than in 2020 (+1.6%). That works out to 31 people per square mile of land. No town dominates: Potosi, the largest, has 2,568 residents, 10.8% of the total. Together its 4 incorporated places hold 13.9% of those residents; the other 86.1% live outside any of them. Reported testing is thin here: 38 tests over 2008 to 2017, or 1.6 for every 1,000 residents (2025 estimate), where Missouri as a whole comes to 9.3.
From Potosi to Caledonia, CDC publishes no figure by town: each reads Washington County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Potosi | 2,568 | +0.5% | 10.8% |
| Irondale | 371 | +1.1% | 1.6% |
| Mineral Point | 235 | +4.0% | 1.0% |
| Caledonia | 134 | +1.5% | 0.6% |
4 incorporated places, 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).
Washington County, Homes
Homes in Washington County
Of Washington County's 10,736 homes, 67% are detached houses, against 70% across Missouri; 28% are mobile homes. Half of its homes were built before 1984, close to Missouri's 1978: 21% date from before 1960 and 22% from 2000 or later. Owners live in 76% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.
| Homes | Washington County | Missouri |
|---|---|---|
| Housing units | 10,736 | 2,809,501 |
| Detached houses | 67% | 70% |
| In buildings of 5 or more | 1% | 13% |
| Mobile homes | 28% | 5% |
| Built before 1960 | 21% | 28% |
| Built since 2000 | 22% | 21% |
| Middle year built | 1984 | 1978 |
| Owner-occupied | 76% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.