Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Washington County, Wisconsin
EPA puts Washington County in Zone 1, its highest radon zone, and high results are common there: 47.9% of the 399 radon tests reported to CDC (2023) came back at or above 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
47.9%
12.2 pts above WI
- Washington
- 47.9%
- Wisconsin
- 35.7%
399 tests, 2023
Median result
3.8pCi/L
Below action level
- Washington
- 3.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
399
13th of 69 by tests
- Washington
- 399
- Dane
- 2,887
Reported to CDC before any fix, 2023
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Wisconsin
14 of 69
Top quarter
- Washington
- 47.9%
- Langlade
- 65.8%
By share, of 69 with 30+ tests
Read a result for Washington County
Starts at Washington County's median, 3.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.8 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Washington County's median reported result, 2023.
The data
Washington County, At a glance
Washington County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Washington County in
USGS geologic potential: High across 100% 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 | 56.3% |
| 2015 | 55.0% |
| 2016 | 50.2% |
| 2017 | 47.9% |
| 2019 | 49.9% |
| 2020 | 45.5% |
| 2021 | 47.8% |
| 2022 | 46.1% |
| 2023 | 47.9% |
2023: 47.9%. Across these years the share ran from 45.5% to 56.3%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 399 tests reported to CDC for Washington County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Washington County, Compared
Washington County radon figures, compared
Calculated by Radon411In Washington County, about 5 in 10 reported tests in 2023 (191 of 399) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 14.5 points higher. Across 72 Wisconsin counties pooled together, 35.7% of tests reached that level, so Washington County runs 12.2 points above its state.
Of 6 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 5 a smaller one; the spread is 19.6% (Fond du Lac County) to 54.9% (Dodge County). By share, Washington County is 14th of 69 Wisconsin counties with 30 or more tests for the same period.
Year by year, 2014 opened at 56.3% and 2023 closed at 47.9% (down 8.4 points), with 2014 the high at 56.3%. Half the tests came in under 3.8 pCi/L and half over it; the single highest reached 45.6 pCi/L. Below the action level, 117 tests (29.3%) came in under 2 pCi/L, against 41.4% statewide, and 91 tests (22.8%) fell between 2 and 4, against 23.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 47.9% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 52 tests taken after mitigation in Washington County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2015, with 919 tests reported; the quietest, 2022, had 258.
Washington CountyWisconsin, pooled
47.9% % of tests35.7% % of tests
| Year | Tests | Washington County, at or above 4 pCi/L | Wisconsin, pooled |
|---|---|---|---|
| 2014 | 689 | 56.3% | 51.1% |
| 2015 | 919 | 55.0% | 51.6% |
| 2016 | 763 | 50.2% | 45.2% |
| 2017 | 511 | 47.9% | 44.8% |
| 2019 | 499 | 49.9% | 42.9% |
| 2020 | 378 | 45.5% | 27.0% |
| 2021 | 314 | 47.8% | 39.9% |
| 2022 | 258 | 46.1% | 42.9% |
| 2023 | 399 | 47.9% | 35.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Washington County, Geology
The ground under Washington County
PredictedUSGS's geologic map puts all of Washington County's mapped land in one class: high radon potential. All of it lies in the area the map calls Eastern Ridges and Lowlands, to which USGS gives a radon index of 12, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Eastern Ridges and Lowlands | Glacial deposits derived from Ordovician carbonate rocks. | High | 12 | 100% |
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
Washington County has more high-potential ground than Wisconsin as a whole: 100% of its land against 34.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Dodge County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Washington County, Local resources
Radon testing and mitigation in Washington County
- Wisconsin's radon programWisconsin Department of Health ServicesWisconsin's radon program does not license radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Wisconsin.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
We recommend starting with your regional Radon Information Center since many centers provide test kits for free or reduced cost, and often with laboratory fees covered.
- Compare kits
- Professionals in Wisconsin19 professionals are listed in Wisconsin.
Listed radon professionals by town: Milwaukee
What Wisconsin's program says
- Phone
- 1-888-569-7236
- DHSRadon@dhs.wisconsin.gov
- Licensing of radon professionals
The State of Wisconsin does not require contractors performing radon measurement or mitigation work to be state licensed or nationally certified.
What it means
Washington County, Questions
Questions about radon in Washington County
Are radon levels high in Washington County?
In 2023, 47.9% of the radon tests reported to CDC for Washington County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.8 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 35.7%.
Which counties border Washington County?
Washington County borders 6 counties: Ozaukee County, Waukesha County, Dodge County, Milwaukee County, Sheboygan County and Fond du Lac County.
Products
Washington County, Products
Testing a home in Washington County
In Washington County, 47.9% of 399 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Washington County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorX-Sense
XR0A-iR Wi-Fi battery radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Wi-Fi
- Screen, app
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Washington County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Washington County
Explore
Washington County, Bordering counties
Counties bordering Washington County
Calculated by Radon411- Radon levels in Dodge CountyEPA zone 1
54.9%at or above 4 pCi/L
Median 4.8 pCi/L · 257 tests · 7.0 points above Washington County
- Radon levels in Ozaukee CountyEPA zone 2
45.8%at or above 4 pCi/L
Median 3.6 pCi/L · 445 tests · 2.1 points below Washington County
- Radon levels in Waukesha CountyEPA zone 1
43.2%at or above 4 pCi/L
Median 3.2 pCi/L · 1,633 tests · 4.7 points below Washington County
- Radon levels in Sheboygan CountyEPA zone 2
42.9%at or above 4 pCi/L
Median 3.3 pCi/L · 399 tests · 5.0 points below Washington County
- Radon levels in Milwaukee CountyEPA zone 2
20.2%at or above 4 pCi/L
Median 1.5 pCi/L · 2,605 tests · 27.7 points below Washington County
- Radon levels in Fond du Lac CountyEPA zone 1
19.6%at or above 4 pCi/L
Median 1.4 pCi/L · 984 tests · 28.3 points below Washington County
Washington County, Cities and towns
Cities and towns in Washington County
The Census Bureau estimates 139,238 residents in Washington County for July 1, 2025, 2,432 more than in 2020 (+1.8%). That works out to 323 people per square mile of land. Milwaukee, the largest place on its list (562,407 residents in all), extends beyond Washington County, so no share of the total is worked out for it. CDC's 399 reported tests for 2023 work out to 2.9 per 1,000 residents (2025 estimate), close to Wisconsin's 3.5.
From Milwaukee to Newburg, CDC publishes no figure by town: each reads Washington County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Milwaukeeextends beyond Washington County | 562,407 | −2.6% | Counted whole |
| West Bend | 32,268 | +1.7% | 23.2% |
| Germantown | 21,050 | +0.6% | 15.1% |
| Hartfordextends beyond Washington County | 16,005 | +2.2% | Counted whole |
| Richfield | 11,785 | +0.3% | 8.5% |
| Jackson | 8,322 | +5.8% | 6.0% |
| Slinger | 6,495 | +7.5% | 4.7% |
| Kewaskumextends beyond Washington County | 4,561 | +5.8% | Counted whole |
| Newburgextends beyond Washington County | 1,129 | −0.6% | Counted whole |
9 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). A place that extends beyond Washington County is counted whole, so it has no share.
Washington County, Homes
Homes in Washington County
Of Washington County's 58,766 homes, 69% are detached houses, against 66% across Wisconsin; 15% are in buildings of five or more homes. Much of Washington County is recent building: 26% of its homes have gone up since 2000 and the middle year built is 1984, against 1975 for Wisconsin. Owners live in 78% of the occupied homes (Wisconsin: 68%), so for most households a test and a fix are their own to order.
| Homes | Washington County | Wisconsin |
|---|---|---|
| Housing units | 58,766 | 2,750,750 |
| Detached houses | 69% | 66% |
| In buildings of 5 or more | 15% | 17% |
| Mobile homes | 1% | 3% |
| Built before 1960 | 20% | 34% |
| Built since 2000 | 26% | 20% |
| Middle year built | 1984 | 1975 |
| Owner-occupied | 78% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.