Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
Locations and reports
Radon Levels in Clay County, Illinois
EPA puts Clay County in Zone 2, its middle radon zone, and only 3 radon tests from it are on file with CDC (2015). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
17.4%
26.3 pts below IL
- Clay
- 17.4%
- Illinois
- 43.7%
69 tests, 2007 to 2016
Median result
1.1pCi/L
Below action level
- Clay
- 1.1 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2007 to 2016
Tests reported
69
80th of 92 by tests
- Clay
- 69
- Cook
- 13,699
Reported to CDC before any fix, 2007 to 2016
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 Illinois
86 of 92
Lowest quarter
- Clay
- 17.4%
- Stark
- 79.4%
By share, of 92 with 30+ tests
Read a result for Clay County
Starts at Clay County's median, 1.1 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.1 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. Clay County's median reported result, 2007 to 2016.
The data
Clay County, At a glance
Clay County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Clay County is a
USGS geologic potential: Moderate across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Clay County, 2015
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 100.0% |
| 2015 | 0.0% |
2015: 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 3 tests were reported to CDC for Clay County over 2015, 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: 2015. Measured data period: 2005 to 2017 (every CDC figure on file).
Clay County, Compared
Clay County radon figures, compared
Calculated by Radon411Clay County's 69 reported tests over the 2007 to 2016 laboratory totals had a middle value of 1.1 pCi/L and a maximum of 23.9 pCi/L, and 17.4% reached 4 pCi/L. Illinois as a whole (102 Illinois counties, pooled) comes to 43.7%: 26.3 points higher than here.
The newest figure, in 2015, counts only 3 tests (0.0% at or above 4 pCi/L), too few to compare, so this reading uses the 69-test figure.
Among its state's counties it ranks 86th of 92 Illinois counties with 30 or more tests for the same period. Statewide for the same period, Stark County reported the highest share (79.4%) and Johnson County the lowest (12.2%).
Below the action level, 46 tests (66.7%) came in under 2 pCi/L, against 31.2% statewide, and 11 tests (15.9%) fell between 2 and 4, against 25.1% statewide. The busiest year on file was 2014, with 12 tests reported; the quietest, 2015, had 3.
EPA's 1993 zone map puts Clay County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.
Next door, the shares run from 14.9% in Wayne County to 39.3% in Effingham County, with Wayne County below Clay County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clay County, Geology
The ground under Clay County
PredictedUSGS's geologic map puts all of Clay County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Southern Central Lowland Province, to which USGS gives a radon index of 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Southern Central Lowland Province | Illinoian glacial deposits, sandstone, and gray shale. | Moderate | 9 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clay County beside the ground around it
Across Illinois 64.5% of the land is rated high; none of Clay County's is. Of the 6 counties that border it, none has as large a share of moderate-potential ground; Effingham County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Clay County, Local resources
Radon testing and mitigation in Clay County
- IEMA-OHS Radon ProgramIEMA-OHS Radon Program, run by Illinois Emergency Management Agency and Office of Homeland Security, licenses or certifies radon professionals and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Illinois.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- Professionals in Illinois339 professionals are listed in Illinois.
What Illinois's program says
- Phone
- (800) 325-1245
- Licensing of radon professionals
The Agency also licenses and regulates the individuals who provide radon measurement and mitigation to the public.
- Disclosure when a home is sold or rented
Illinois Radon Awareness Act - This is the legislation that requires the seller to provide to the buyer of any interest in residential real property the IEMA-OHS pamphlet entitled "Radon Testing Guidelines for Real Estate Transactions" and the Illinois Disclosure of Information on Radon Hazards.
What it means
Clay County, Questions
Questions about radon in Clay County
Are radon levels high in Clay County?
In 2015, 0.0% of the radon tests reported to CDC for Clay County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.4 pCi/L. Of 92 Illinois counties with 30 or more tests for the same period, 85 reported a higher share; pooled, the state comes to 43.7%.
Which counties border Clay County?
Clay County borders 6 counties: Effingham County, Richland County, Marion County, Jasper County, Wayne County and Fayette County.
Products
Clay County, Products
Testing a home in Clay County
In Clay County, 17.4% of 69 tests reported to CDC over the 2007 to 2016 laboratory totals reached 4 pCi/L, against 43.7% pooled across Illinois. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Clay 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
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
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Clay County, Bordering counties
Counties bordering Clay County
Calculated by Radon411- Radon levels in Effingham CountyEPA zone 2
39.3%at or above 4 pCi/L
Median 3.1 pCi/L · 702 tests · 21.9 points above Clay County
- Radon levels in Fayette CountyEPA zone 2
35.0%at or above 4 pCi/L
Median 2.9 pCi/L · 120 tests · 17.6 points above Clay County
- Radon levels in Jasper CountyEPA zone 2
21.1%at or above 4 pCi/L
Median 1.8 pCi/L · 71 tests · 3.7 points above Clay County
- Radon levels in Marion CountyEPA zone 2
19.9%at or above 4 pCi/L
Median 1.8 pCi/L · 387 tests · 2.5 points above Clay County
- Radon levels in Richland CountyEPA zone 2
19.3%at or above 4 pCi/L
Median 1.9 pCi/L · 140 tests · 1.9 points above Clay County
- Radon levels in Wayne CountyEPA zone 2
14.9%at or above 4 pCi/L
Median 1.4 pCi/L · 87 tests · 2.5 points below Clay County
Clay County, Cities and towns
Cities and towns in Clay County
About 12,793 people live in Clay County by the Census Bureau's estimate for July 1, 2025, 478 fewer than in 2020 (−3.6%). That works out to 27 people per square mile of land. Its largest town, Flora, has 4,634 residents, 36.2% of the total. Together its 6 incorporated places hold 55.5% of those residents; the other 44.5% live outside any of them. Reported testing is thin here: 69 tests over 2007 to 2016, or 5.4 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 8.3.
From Flora to Sailor Springs, CDC publishes no figure by town: each reads Clay County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Flora | 4,634 | −3.5% | 36.2% |
| Louisville | 1,108 | −3.5% | 8.7% |
| Clay City | 816 | −4.0% | 6.4% |
| Xenia | 360 | −4.0% | 2.8% |
| Iola | 96 | −4.0% | 0.8% |
| Sailor Springs | 87 | −3.3% | 0.7% |
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).
Clay County, Homes
Homes in Clay County
Of Clay County's 6,147 homes, 73% are detached houses, against 58% across Illinois; 19% are mobile homes. Half of its homes were built before 1973, close to Illinois' 1970: 37% date from before 1960 and 18% from 2000 or later. Owners live in 81% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Clay County | Illinois |
|---|---|---|
| Housing units | 6,147 | 5,443,501 |
| Detached houses | 73% | 58% |
| In buildings of 5 or more | 4% | 22% |
| Mobile homes | 19% | 2% |
| Built before 1960 | 37% | 38% |
| Built since 2000 | 18% | 16% |
| Middle year built | 1973 | 1970 |
| Owner-occupied | 81% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.