Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
Locations and reports
Radon Levels in Clark County, Missouri
EPA puts Clark 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
Highest bordering
43.6%
Lee County
- Lee
- 43.6%
- Van Buren
- 32.1%
4 of 6 neighbours have 30+ tests, 2008 to 2017
Nearest county
32.4%
Lewis County, 22 miles
- Lewis
- 32.4%
- Missouri
- 30.6%
Share at 4+ pCi/L, 71 tests, 2008 to 2017
Ground above low
100.0%
5.8 pts above Missouri
- Clark
- 100.0%
- Missouri
- 94.2%
Share of land USGS rates moderate or high potential
Tests reported
21
Too few for a share
- Clark
- 21
- Needed
- 30
2006 to 2015, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Clark County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
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 93% 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 | 0.0% |
| 2015 | 50.0% |
| 2018 | 100.0% |
| 2021 | 25.0% |
| 2022 | 0.0% |
| 2023 | 0.0% |
2023: 0.0%. 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 Clark 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).
Clark County, Compared
Clark County radon figures, compared
Calculated by Radon411CDC's largest figure for Clark County rests on 21 tests over the 2006 to 2015 laboratory totals, 6 of them at or above 4 pCi/L, so each test moves its share by 4.8 points and no rank or comparison is drawn from it. Results reached as high as 21.0 pCi/L, with a middle value of 1.5 pCi/L.
Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Lee County, IA reported the largest share at or above 4 pCi/L, 43.6%, and Van Buren County, IA the smallest, 32.1%, with Hancock County, IL at 43.5% and Lewis County at 32.4% between. Farther out, Marion County (42 miles away) at 41.8%, Adair County (48 miles away) at 27.2% and Macon County (59 miles away) at 19.4% have figures too. Pooled across 115 Missouri counties, 30.6% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, Atchison County reported the highest share (69.9%) and Vernon County the lowest (8.8%). EPA's 1993 map puts Clark County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 93% of the county's land moderate radon potential.
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: 93.4% of its land is moderate radon potential, with 6.6% high. The map puts 93.4% of Clark County in the area it calls Dissected Till Plains and 6.5% in Galesburg Plain. 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 |
|---|---|---|---|---|
| Dissected Till Plains | Till-covered Pennsylvanian sandstone, shale, and limestone. | Moderate | 11 | 93.4% |
| Galesburg Plain | Illinoian glacial deposits and loess over Paleozoic sedimentary rocks. | High | 13 | 6.5% |
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
On high-potential ground Clark County is close to Missouri as a whole: 6.6% of its land against 8.2%. Of the 6 counties that border it, 4 have more high-potential ground, Hancock County, IL the most at 100%.
The map rates the ground, not the air in any home.
Local help
Clark County, Local resources
Radon testing and mitigation in Clark 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
Clark County, Questions
Questions about radon in Clark County
Are radon levels high in Clark County?
In 2023, 0.0% of the radon tests reported to CDC for Clark County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.6 pCi/L. Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Lee County, IA reported the largest share at or above 4 pCi/L, 43.6%, and Van Buren County, IA the smallest, 32.1%, with Hancock County, IL at 43.5% and Lewis County at 32.4% between.
Which counties border Clark County?
Clark County borders 6 counties: Lee County, IA, Scotland County, MO, Van Buren County, IA, Lewis County, MO, Knox County, MO and Hancock County, IL.
Products
Clark County, Products
Testing a home in Clark County
No CDC figure names Clark County; the nearest county with one, Lewis County (22 miles away), reported 32.4% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. 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
Monitor
EcoBlu plug-in digital radon monitor with a display
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
Method: Ion chamber
First reading: Within 10 minutes
- 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 Lee County, IAEPA zone 1
43.6%at or above 4 pCi/L
Median 3.2 pCi/L · 351 tests
- Radon levels in Hancock County, ILEPA zone 1
43.5%at or above 4 pCi/L
Median 3.5 pCi/L · 177 tests
- Radon levels in Lewis County, MOEPA zone 2
32.4%at or above 4 pCi/L
Median 2.6 pCi/L · 71 tests
- Radon levels in Van Buren County, IAEPA zone 1
32.1%at or above 4 pCi/L
Median 2.3 pCi/L · 56 tests
- Radon levels in Scotland County, MOEPA zone 2
16.7%at or above 4 pCi/L
Median 1.4 pCi/L · 18 tests
- Radon levels in Knox County, MOEPA zone 2
0.0%at or above 4 pCi/L
Median 1.9 pCi/L · 10 tests
Clark County, Cities and towns
Cities and towns in Clark County
About 6,475 people live in Clark County by the Census Bureau's estimate for July 1, 2025, 189 fewer than in 2020 (−2.8%). That works out to 13 people per square mile of land. Its largest town, Kahoka, has 1,962 residents, 30.3% of the total. Together its 6 incorporated places hold 43.4% of those residents; the other 56.6% live outside any of them. Reported testing is thin here: 21 tests over 2006 to 2015, or 3.2 for every 1,000 residents (2025 estimate), where Missouri as a whole comes to 7.7.
From Kahoka to Luray, CDC publishes no figure by town: each reads Clark County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Kahoka | 1,962 | −0.7% | 30.3% |
| Wayland | 399 | −2.0% | 6.2% |
| Wyaconda | 204 | −4.7% | 3.2% |
| Alexandria | 102 | −3.8% | 1.6% |
| Revere | 73 | −3.9% | 1.1% |
| Luray | 69 | −2.8% | 1.1% |
6 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).
Clark County, Homes
Homes in Clark County
Clark County is a place of houses on their own lots: 78% of its 3,233 homes are detached single-family houses, against 70% across Missouri. The homes are older than Missouri's as a whole: half were built before 1969 (1978 for Missouri), and 36% date from before 1960. Owners live in 78% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.
| Homes | Clark County | Missouri |
|---|---|---|
| Housing units | 3,233 | 2,809,501 |
| Detached houses | 78% | 70% |
| In buildings of 5 or more | under 1% | 13% |
| Mobile homes | 15% | 5% |
| Built before 1960 | 36% | 28% |
| Built since 2000 | 12% | 21% |
| Middle year built | 1969 | 1978 |
| 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.