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
Locations and reports
Radon Levels in Clarke County, Iowa
EPA puts Clarke County in Zone 1, its highest radon zone, and high results are common there: 45.8% of the 120 radon tests reported to CDC (2008 to 2017, laboratory totals) 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
45.8%
12.7 pts below IA
- Clarke
- 45.8%
- Iowa
- 58.5%
120 tests, 2008 to 2017
Median result
3.5pCi/L
Below action level
- Clarke
- 3.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
120
88th of 99 by tests
- Clarke
- 120
- Polk
- 10,945
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Iowa
85 of 99
Lowest quarter
- Clarke
- 45.8%
- Sioux
- 84.2%
By share, of 99 with 30+ tests
Read a result for Clarke County
Starts at Clarke County's median, 3.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.5 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. Clarke County's median reported result, 2008 to 2017.
The data
Clarke County, At a glance
Clarke County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Clarke 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 Clarke County, 2008 to 2017, laboratory
Under 2 pCi/L: 27%2 to 4 pCi/L: 27%4 pCi/L and above: 46%
Of 120 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 33 | 27.5% |
| 2 to 4 pCi/L | 32 | 26.7% |
| 4 pCi/L and above | 55 | 45.8% |
What these figures count
These are the 120 tests reported to CDC for Clarke County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Clarke County, Compared
Clarke County radon figures, compared
Calculated by Radon411In Clarke County, about 5 in 10 reported tests over the 2008 to 2017 laboratory totals (55 of 120) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 10.1 points higher. Across 99 Iowa counties pooled together, 58.5% of tests reached that level, so Clarke County runs 12.7 points below its state.
Of 7 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 25.9% (Decatur County) to 66.0% (Warren County). By share, Clarke County is 85th of 99 Iowa counties with 30 or more tests for the same period.
Half the tests came in under 3.5 pCi/L and half over it; the single highest reached 37.2 pCi/L. Below the action level, 33 tests (27.5%) came in under 2 pCi/L, against 21.8% statewide, and 32 tests (26.7%) fell between 2 and 4, against 19.7% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 45.8% share point the same way here. USGS geology rates 100% of the county's land high radon potential.
CDC's ten-year totals for Clarke County went from 114 tests (2005 to 2014) to 120 (2008 to 2017), the share going from 40.4% to 45.8%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clarke County, Geology
The ground under Clarke County
PredictedUSGS's geologic map puts all of Clarke County's mapped land in one class: high radon potential. All of it lies in the area the map calls Loess-Covered Drift Plains, to which USGS gives a radon index of 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Loess-Covered Drift Plains | Pre-Illinoian and Illinoian glacial deposits, and loess. | High | 13 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clarke County beside the ground around it
On high-potential ground Clarke County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Lucas County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Clarke County, Local resources
Radon testing and mitigation in Clarke County
- Iowa HHS Radon ProgramIowa HHS Radon Program, run by Iowa Department of Health and Human Services, licenses or certifies radon professionals, offers free or discounted test kits and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Iowa.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
You can reach the Hotline by calling 1-800-383-5992 to order low-cost radon test kits and find answers to your radon questions.
- Compare kits
- Professionals in Iowa185 professionals are listed in Iowa.
What Iowa's program says
- Phone
- (515) 281-4928
- Licensing of radon professionals
Iowa’s radon program approves applications for persons who wish to become certified to perform radon testing or credentialed to perform mitigation and laboratories that provide radon testing devices and analytical services.
- Disclosure when a home is sold or rented
However, per Iowa Code chapters 543B.9 and 543B.18 and Iowa Administrative Code 193E Chapter 14 administered by the Iowa Real Estate Commission, a seller must disclose any known tests for the presence of radon and if yes, provide the date of last report and the result(s).
What it means
Clarke County, Questions
Questions about radon in Clarke County
Are radon levels high in Clarke County?
Over the 2008 to 2017 laboratory totals, 45.8% of the radon tests reported to CDC for Clarke County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.5 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 84 reported a higher share; pooled, the state comes to 58.5%.
Which counties border Clarke County?
Clarke County borders 7 counties: Decatur County, Warren County, Union County, Lucas County, Madison County, Wayne County and Ringgold County.
Products
Clarke County, Products
Testing a home in Clarke County
In Clarke County, 45.8% of 120 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across Iowa. In Zone 1 the year-round level in Clarke 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
MonitorKidde
Radon Detector (RAB) battery digital radon detector with an alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Clarke County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Clarke County
Explore
Clarke County, Bordering counties
Counties bordering Clarke County
Calculated by Radon411- Radon levels in Warren CountyEPA zone 1
66.0%at or above 4 pCi/L
Median 6.3 pCi/L · 1,513 tests · 20.2 points above Clarke County
- Radon levels in Madison CountyEPA zone 1
62.3%at or above 4 pCi/L
Median 6.0 pCi/L · 318 tests · 16.5 points above Clarke County
- Radon levels in Union CountyEPA zone 1
61.8%at or above 4 pCi/L
Median 4.9 pCi/L · 131 tests · 16.0 points above Clarke County
- Radon levels in Lucas CountyEPA zone 1
39.3%at or above 4 pCi/L
Median 3.3 pCi/L · 84 tests · 6.5 points below Clarke County
- Radon levels in Wayne CountyEPA zone 1
34.8%at or above 4 pCi/L
Median 3.0 pCi/L · 46 tests · 11.0 points below Clarke County
- Radon levels in Ringgold CountyEPA zone 1
28.7%at or above 4 pCi/L
Median 2.6 pCi/L · 87 tests · 17.1 points below Clarke County
- Radon levels in Decatur CountyEPA zone 1
25.9%at or above 4 pCi/L
Median 2.5 pCi/L · 85 tests · 19.9 points below Clarke County
Clarke County, Cities and towns
Cities and towns in Clarke County
About 9,574 people live in Clarke County by the Census Bureau's estimate for July 1, 2025, 157 fewer than in 2020 (−1.6%). That works out to 22 people per square mile of land. Osceola alone is home to 5,679 of them, 59.3% of the total. Together its 3 incorporated places hold 67.0% of those residents; the other 33.0% live outside any of them. Reported testing is thin here: 120 tests over 2008 to 2017, or 12.5 for every 1,000 residents (2025 estimate), where Iowa as a whole comes to 29.4.
From Osceola to Woodburn, CDC publishes no figure by town: each reads Clarke County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Osceola | 5,679 | +4.9% | 59.3% |
| Murray | 600 | −11.8% | 6.3% |
| Woodburn | 133 | −8.9% | 1.4% |
3 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).
Clarke County, Homes
Homes in Clarke County
Of Clarke County's 4,401 homes, 71% are detached houses, against 72% across Iowa; 12% are in buildings of five or more homes. Half of its homes were built before 1975, close to Iowa's 1971: 32% date from before 1960 and 20% from 2000 or later. 69% of occupied homes are lived in by their owner (Iowa: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Clarke County | Iowa |
|---|---|---|
| Housing units | 4,401 | 1,427,175 |
| Detached houses | 71% | 72% |
| In buildings of 5 or more | 12% | 14% |
| Mobile homes | 7% | 3% |
| Built before 1960 | 32% | 39% |
| Built since 2000 | 20% | 21% |
| Middle year built | 1975 | 1971 |
| Owner-occupied | 69% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.