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 Clark County, Wisconsin
EPA puts Clark County in Zone 2, its middle radon zone, and 25.3% of its 75 reported radon tests (2023) were 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
25.3%
10.4 pts below WI
- Clark
- 25.3%
- Wisconsin
- 35.7%
75 tests, 2023
Median result
2.2pCi/L
Below action level
- Clark
- 2.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
75
49th of 69 by tests
- Clark
- 75
- Dane
- 2,887
Reported to CDC before any fix, 2023
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 Wisconsin
54 of 69
Lowest quarter
- Clark
- 25.3%
- Langlade
- 65.8%
By share, of 69 with 30+ tests
Read a result for Clark County
Starts at Clark County's median, 2.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.2 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. Clark County's median reported result, 2023.
The data
Clark County, At a glance
Clark County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Clark County is a
USGS geologic potential: Moderate across 97% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Clark County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 33.3% |
| 2015 | 35.5% |
| 2016 | 35.7% |
| 2017 | 28.8% |
| 2019 | 21.2% |
| 2020 | 18.6% |
| 2021 | 50.0% |
| 2022 | 38.0% |
| 2023 | 25.3% |
2023: 25.3%. Across these years the share ran from 18.6% to 50.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 75 tests reported to CDC for Clark 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).
Clark County, Compared
Clark County radon figures, compared
Calculated by Radon411Clark County's 75 reported tests in 2023 had a middle value of 2.2 pCi/L and a maximum of 11.4 pCi/L, and 25.3% reached 4 pCi/L. Wisconsin as a whole (72 Wisconsin counties, pooled) comes to 35.7%: 10.4 points higher than here.
Among its state's counties it ranks 54th of 69 Wisconsin counties with 30 or more tests for the same period. Statewide for the same period, Langlade County reported the highest share (65.8%) and Bayfield County the lowest (5.7%).
Below the action level, 33 tests (44.0%) came in under 2 pCi/L, against 41.4% statewide, and 23 tests (30.7%) fell between 2 and 4, against 23.0% statewide. The busiest year on file was 2020, with 97 tests reported; the quietest, 2021, had 18.
EPA's 1993 zone map puts Clark County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 97% of the county's land moderate radon potential.
Next door, the shares run from 18.3% in Wood County to 51.9% in Marathon County, with Taylor County and Wood County below Clark County. Over 8 years of annual figures the share fell 8.0 points, from 33.3% in 2014 to 25.3% in 2023; its peak was 38.0% in 2022.
Clark CountyWisconsin, pooled
25.3% % of tests35.7% % of tests
| Year | Tests | Clark County, at or above 4 pCi/L | Wisconsin, pooled |
|---|---|---|---|
| 2014 | 51 | 33.3% | 51.1% |
| 2015 | 31 | 35.5% | 51.6% |
| 2016 | 56 | 35.7% | 45.2% |
| 2017 | 52 | 28.8% | 44.8% |
| 2019 | 52 | 21.2% | 42.9% |
| 2020 | 97 | 18.6% | 27.0% |
| 2022 | 50 | 38.0% | 42.9% |
| 2023 | 75 | 25.3% | 35.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clark County, Geology
The ground under Clark County
PredictedMost of the ground under Clark County is one class on USGS's geologic map: 97.5% of its land is moderate radon potential, with 2.5% high. The map puts 93.2% of Clark County in the area it calls Central Plain/Northern Highland and 3.5% in Chippewa, Wisconsin Valley, and Langlade sublobes of the Superior Lobe, with 2 smaller areas beside them. USGS gives both a radon index of 10, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Central Plain/Northern Highland | Pre-Late Wisconsinan glacial deposits derived from sandstone and carbonate rocks. | Moderate | 10 | 93.2% |
| Chippewa, Wisconsin Valley, and Langlade sublobes of the Superior Lobe | Granite, granite-derived glacial deposits, and mafic volcanic rocks. | Moderate | 10 | 3.5% |
| Wolf River Batholith | Plutonic granitic rocks including quartz monzonite, syenite, monzonite, anorthosite. | High | 13 | 2.5% |
| Driftless Area | Cambrian sandstone. | Moderate | 10 | 0.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clark County beside the ground around it
Wisconsin as a whole has more high-potential ground than Clark County: 34.8% of its land, against 2.5% here. Of the 6 counties that border it, 2 have more high-potential ground, Marathon County the most at 84.0%.
The map rates the ground, not the air in any home.
Local help
Clark County, Local resources
Radon testing and mitigation in Clark 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.
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
Clark County, Questions
Questions about radon in Clark County
Are radon levels high in Clark County?
In 2023, 25.3% of the radon tests reported to CDC for Clark County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.2 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 53 reported a higher share; pooled, the state comes to 35.7%.
Which counties border Clark County?
Clark County borders 6 counties: Jackson County, Taylor County, Eau Claire County, Wood County, Chippewa County and Marathon County.
Products
Clark County, Products
Testing a home in Clark County
In Clark County, 25.3% of 75 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Clark County; a long-term test tells the year-round average.
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
MonitorPYZYCKYH
RD17 plug-in radon detector with a rechargeable battery and color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Clark County, Bordering counties
Counties bordering Clark County
Calculated by Radon411- Radon levels in Marathon CountyEPA zone 1
51.9%at or above 4 pCi/L
Median 4.3 pCi/L · 349 tests · 26.6 points above Clark County
- Radon levels in Jackson CountyEPA zone 2
38.7%at or above 4 pCi/L
Median 3.2 pCi/L · 93 tests · 13.4 points above Clark County
- Radon levels in Chippewa CountyEPA zone 2
35.7%at or above 4 pCi/L
Median 2.5 pCi/L · 311 tests · 10.4 points above Clark County
- Radon levels in Eau Claire CountyEPA zone 2
32.7%at or above 4 pCi/L
Median 2.8 pCi/L · 474 tests · 7.4 points above Clark County
- Radon levels in Taylor CountyEPA zone 2
18.9%at or above 4 pCi/L
Median 2.1 pCi/L · 37 tests · 6.4 points below Clark County
- Radon levels in Wood CountyEPA zone 1
18.3%at or above 4 pCi/L
Median 1.4 pCi/L · 208 tests · 7.0 points below Clark County
Clark County, Cities and towns
Cities and towns in Clark County
The Census Bureau estimates 35,052 residents in Clark County for July 1, 2025, 412 more than in 2020 (+1.2%). That works out to 29 people per square mile of land. Stanley, the largest place on its list (3,876 residents in all), extends beyond Clark County, so no share of the total is worked out for it. Reported testing is thin here: 75 tests over 2023, or 2.1 for every 1,000 residents (2025 estimate), where Wisconsin as a whole comes to 3.5.
From Stanley to Curtiss, CDC publishes no figure by town: each reads Clark County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Stanleyextends beyond Clark County | 3,876 | +1.8% | Counted whole |
| Abbotsfordextends beyond Clark County | 2,413 | +5.4% | Counted whole |
| Neillsville | 2,367 | −0.6% | 6.8% |
| Colbyextends beyond Clark County | 1,957 | −1.8% | Counted whole |
| Thorp | 1,781 | −0.4% | 5.1% |
| Loyal | 1,190 | −1.0% | 3.4% |
| Greenwood | 1,079 | +1.8% | 3.1% |
| Owen | 904 | −1.1% | 2.6% |
| Dorchesterextends beyond Clark County | 840 | −0.9% | Counted whole |
| Withee | 527 | +4.2% | 1.5% |
| Granton | 368 | −3.4% | 1.0% |
| Unityextends beyond Clark County | 368 | −2.4% | Counted whole |
- Curtiss
13 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Clark County is counted whole, so it has no share.
Clark County, Homes
Homes in Clark County
Clark County is a place of houses on their own lots: 82% of its 14,842 homes are detached single-family houses, against 66% across Wisconsin. Half of its homes were built before 1971, close to Wisconsin's 1975: 41% date from before 1960 and 17% from 2000 or later. 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 | Clark County | Wisconsin |
|---|---|---|
| Housing units | 14,842 | 2,750,750 |
| Detached houses | 82% | 66% |
| In buildings of 5 or more | 6% | 17% |
| Mobile homes | 7% | 3% |
| Built before 1960 | 41% | 34% |
| Built since 2000 | 17% | 20% |
| Middle year built | 1971 | 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.