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 Monroe County, Illinois
EPA puts Monroe County in Zone 2, its middle radon zone, and 39.9% of its 714 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
39.9%
6.2 pts above IL
- Monroe
- 39.9%
- Illinois
- 33.7%
714 tests, 2017
Median result
3.0pCi/L
Below action level
- Monroe
- 3.0 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
714
22nd of 70 by tests
- Monroe
- 714
- 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
43 of 70
Middle half
- Monroe
- 39.9%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Monroe County
Starts at Monroe County's median, 3.0 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.0 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. Monroe County's median reported result, 2017.
The data
Monroe County, At a glance
Monroe County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Monroe 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 Monroe County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 44.6% |
| 2015 | 34.8% |
| 2016 | 50.0% |
| 2017 | 39.9% |
2017: 39.9%. Across these years the share ran from 34.8% to 50.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 714 tests reported to CDC for Monroe 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).
Monroe County, Compared
Monroe County radon figures, compared
Calculated by Radon411In Monroe County, about 4 in 10 reported tests in 2017 (285 of 714) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 8.2 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Monroe County runs 6.2 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 30.1% (St. Louis County, MO) to 47.4% (Jefferson County, MO). By share, Monroe County is 43rd of 70 Illinois counties with 30 or more tests for the same period.
Year by year, 2014 opened at 44.6% and 2017 closed at 39.9% (down 4.7 points), with 2014 the high at 44.6%. Half the tests came in under 3.0 pCi/L and half over it; the single highest reached 33.9 pCi/L. Below the action level, 195 tests (27.3%) came in under 2 pCi/L, against 37.7% statewide, and 234 tests (32.8%) 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 39.9% 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 1,008 tests reported; the quietest, 2016, had 6.
Monroe CountyIllinois, pooled
| Year | Tests | Monroe County, at or above 4 pCi/L | Illinois, pooled |
|---|---|---|---|
| 2014 | 1,008 | 44.6% | 37.8% |
| 2015 | 612 | 34.8% | 36.6% |
| 2017 | 714 | 39.9% | 33.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Monroe County, Geology
The ground under Monroe County
PredictedUSGS's geologic map puts all of Monroe County's mapped land in one class: moderate radon potential. The map puts 63.1% of Monroe County in the area it calls Southern Central Lowland Province and 36.9% 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 | 63.1% |
| Salem Plateau | Ordovician dolomite, sandstone, limestone, and shale. | Moderate | 11 | 36.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Monroe County beside the ground around it
Across Illinois 64.5% of the land is rated high; none of Monroe County's is. Of the 5 counties that border it, none has as large a share of moderate-potential ground; Randolph County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Monroe County, Local resources
Radon testing and mitigation in Monroe County
Listed radon businesses with an address in Monroe 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.
Listed radon professionals by town: Waterloo
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
Monroe County, Questions
Questions about radon in Monroe County
Are radon levels high in Monroe County?
In 2017, 39.9% of the radon tests reported to CDC for Monroe County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.0 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 42 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Monroe County?
Monroe County borders 5 counties: St. Clair County, IL, Jefferson County, MO, Ste. Genevieve County, MO, Randolph County, IL and St. Louis County, MO.
Products
Monroe County, Products
Testing a home in Monroe County
In Monroe County, 39.9% of 714 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 Monroe 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
Monroe County, Bordering counties
Counties bordering Monroe County
Calculated by Radon411- Radon levels in Jefferson County, MOEPA zone 2
47.4%at or above 4 pCi/L
Median 3.6 pCi/L · 133 tests · 7.5 points above Monroe County
42.9%at or above 4 pCi/L
Median 2.1 pCi/L · 14 tests · 3.0 points above Monroe County
- Radon levels in Randolph County, ILEPA zone 2
35.0%at or above 4 pCi/L
Median 2.9 pCi/L · 60 tests · 4.9 points below Monroe 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 · 6.2 points below Monroe County
- Radon levels in St. Louis County, MOEPA zone 2
30.1%at or above 4 pCi/L
Median 2.6 pCi/L · 459 tests · 9.8 points below Monroe County
Monroe County, Cities and towns
Cities and towns in Monroe County
Monroe County's population has barely moved since 2020: 34,840 residents on July 1, 2025 against 34,961 then, by the Census Bureau's estimates. That works out to 90 people per square mile of land. Its largest town, Waterloo, has 11,132 residents, 32.0% of the total. Testing is reported here more often than across the state: CDC's 714 reported tests for 2017 come to 20.5 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.
From Waterloo to Fults, CDC publishes no figure by town: each reads Monroe County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Waterloo | 11,132 | +1.3% | 32.0% |
| Columbiaextends beyond Monroe County | 10,865 | −1.6% | Counted whole |
| Dupoextends beyond Monroe County | 3,766 | −5.4% | Counted whole |
| Valmeyer | 1,204 | −1.7% | 3.5% |
| Heckerextends beyond Monroe County | 418 | −2.8% | Counted whole |
| Maeystown | 151 | −0.7% | 0.4% |
| Fults | 27 | −3.6% | Under 0.1% |
7 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). A place that extends beyond Monroe County is counted whole, so it has no share.
Monroe County, Homes
Homes in Monroe County
Monroe County is a place of houses on their own lots: 83% of its 14,665 homes are detached single-family houses, against 58% across Illinois. Much of Monroe County is recent building: 32% of its homes have gone up since 2000 and the middle year built is 1990, against 1970 for Illinois. Owners live in 84% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Monroe County | Illinois |
|---|---|---|
| Housing units | 14,665 | 5,443,501 |
| Detached houses | 83% | 58% |
| In buildings of 5 or more | 8% | 22% |
| Mobile homes | 2% | 2% |
| Built before 1960 | 21% | 38% |
| Built since 2000 | 32% | 16% |
| Middle year built | 1990 | 1970 |
| Owner-occupied | 84% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.