Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
Locations and reports
Radon Levels in Randolph County, Illinois
EPA puts Randolph County in Zone 2, its middle radon zone, and 35.0% of its 60 reported radon tests (2017) 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
35.0%
1.3 pts above IL
- Randolph
- 35.0%
- Illinois
- 33.7%
60 tests, 2017
Median result
2.9pCi/L
Below action level
- Randolph
- 2.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
60
58th of 70 by tests
- Randolph
- 60
- Cook
- 26,937
Reported to CDC before any fix, 2017
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
49 of 70
Middle half
- Randolph
- 35.0%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Randolph County
Starts at Randolph County's median, 2.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.9 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. Randolph County's median reported result, 2017.
The data
Randolph County, At a glance
Randolph County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Randolph 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 Randolph County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 20.0% |
| 2015 | 41.7% |
| 2016 | 0.0% |
| 2017 | 35.0% |
2017: 35.0%. Across these years the share ran from 0.0% to 41.7%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 60 tests reported to CDC for Randolph County over 2017, 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: 2017. Measured data period: 2005 to 2017 (every CDC figure on file).
Randolph County, Compared
Randolph County radon figures, compared
Calculated by Radon411In Randolph County, about 4 in 10 reported tests in 2017 (21 of 60) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 3.3 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Randolph County runs 1.3 points above its state.
Of 4 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 11.8% (Washington County) to 39.9% (Monroe County). By share, Randolph County is 49th of 70 Illinois counties with 30 or more tests for the same period.
Year by year, 2014 opened at 20.0% and 2017 closed at 35.0% (up 15.0 points), with 2015 the high at 41.7%. Half the tests came in under 2.9 pCi/L and half over it; the single highest reached 15.6 pCi/L. Below the action level, 24 tests (40.0%) came in under 2 pCi/L, against 37.7% statewide, and 15 tests (25.0%) fell between 2 and 4, against 28.6% statewide.
Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 35.0% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential.
The busiest year on file was 2014, with 60 tests reported; the quietest, 2016, had 3.
Randolph CountyIllinois, pooled
| Year | Tests | Randolph County, at or above 4 pCi/L | Illinois, pooled |
|---|---|---|---|
| 2014 | 60 | 20.0% | 37.8% |
| 2015 | 36 | 41.7% | 36.6% |
| 2017 | 60 | 35.0% | 33.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Randolph County, Geology
The ground under Randolph County
PredictedUSGS's geologic map puts all of Randolph County's mapped land in one class: moderate radon potential. The map puts 83.8% of Randolph County in the area it calls Southern Central Lowland Province and 16.2% in Salem Plateau. USGS gives the first a radon index of 9 and the second 11, both 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 | 83.8% |
| Salem Plateau | Ordovician dolomite, sandstone, limestone, and shale. | Moderate | 11 | 16.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Randolph County beside the ground around it
Across Illinois 64.5% of the land is rated high; none of Randolph County's is. Of the 7 counties that border it, none has as large a share of moderate-potential ground; Jackson County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Randolph County, Local resources
Radon testing and mitigation in Randolph 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
Randolph County, Questions
Questions about radon in Randolph County
Are radon levels high in Randolph County?
In 2017, 35.0% of the radon tests reported to CDC for Randolph County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.9 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 48 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Randolph County?
Randolph County borders 7 counties: Perry County, MO, Ste. Genevieve County, MO, Perry County, IL, Jackson County, IL, Monroe County, IL, Washington County, IL and St. Clair County, IL.
Products
Randolph County, Products
Testing a home in Randolph County
In Randolph County, 35.0% of 60 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Randolph County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
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
MonitorX-Sense
XR0A-SR battery digital radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Screen
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
Randolph County, Bordering counties
Counties bordering Randolph County
Calculated by Radon41142.9%at or above 4 pCi/L
Median 2.1 pCi/L · 14 tests · 7.9 points above Randolph County
- Radon levels in Perry County, ILEPA zone 2
40.0%at or above 4 pCi/L
Median 1.5 pCi/L · 15 tests · 5.0 points above Randolph County
- Radon levels in Monroe County, ILEPA zone 2
39.9%at or above 4 pCi/L
Median 3.0 pCi/L · 714 tests · 4.9 points above Randolph County
- Radon levels in St. Clair County, ILEPA zone 2
33.7%at or above 4 pCi/L
Median 2.6 pCi/L · 5,193 tests · 1.3 points below Randolph County
- Radon levels in Perry County, MOEPA zone 2
33.3%at or above 4 pCi/L
Median 3.6 pCi/L · 3 tests · 1.7 points below Randolph County
- Radon levels in Jackson County, ILEPA zone 2
25.0%at or above 4 pCi/L
Median 2.5 pCi/L · 96 tests · 10.0 points below Randolph County
- Radon levels in Washington County, ILEPA zone 2
11.8%at or above 4 pCi/L
Median 2.0 pCi/L · 51 tests · 23.2 points below Randolph County
Randolph County, Cities and towns
Cities and towns in Randolph County
About 29,921 people live in Randolph County by the Census Bureau's estimate for July 1, 2025, 170 fewer than in 2020 (−0.6%). That works out to 52 people per square mile of land. Its largest town, Chester, has 6,847 residents, 22.9% of the total. Together its 14 incorporated places hold 70.3% of those residents; the other 29.7% live outside any of them. Reported testing is thin here: 60 tests over 2017, or 2.0 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Chester to Kaskaskia, CDC publishes no figure by town: each reads Randolph County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Chester | 6,847 | +0.4% | 22.9% |
| Sparta | 4,022 | −1.4% | 13.4% |
| Red Bud | 3,761 | −0.7% | 12.6% |
| Steeleville | 1,883 | −1.8% | 6.3% |
| Percy | 905 | −0.7% | 3.0% |
| Coulterville | 825 | −0.5% | 2.8% |
| Tilden | 745 | −0.1% | 2.5% |
| Evansville | 533 | −1.8% | 1.8% |
| Prairie du Rocher | 510 | +2.2% | 1.7% |
| Ellis Grove | 324 | −0.3% | 1.1% |
| Baldwin | 313 | −1.6% | 1.0% |
| Ruma | 313 | −1.3% | 1.0% |
- Rockwood
- Kaskaskia
14 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).
Randolph County, Homes
Homes in Randolph County
Randolph County is a place of houses on their own lots: 76% of its 13,400 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1972, close to Illinois' 1970: 36% date from before 1960 and 14% from 2000 or later. Owners live in 77% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Randolph County | Illinois |
|---|---|---|
| Housing units | 13,400 | 5,443,501 |
| Detached houses | 76% | 58% |
| In buildings of 5 or more | 3% | 22% |
| Mobile homes | 14% | 2% |
| Built before 1960 | 36% | 38% |
| Built since 2000 | 14% | 16% |
| Middle year built | 1972 | 1970 |
| Owner-occupied | 77% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.