Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Marion County, Illinois
EPA puts Marion County in Zone 2, its middle radon zone, and 20.0% of its 45 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
20.0%
13.7 pts below IL
- Marion
- 20.0%
- Illinois
- 33.7%
45 tests, 2017
Median result
1.9pCi/L
Below action level
- Marion
- 1.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
45
63rd of 70 by tests
- Marion
- 45
- 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
65 of 70
Lowest quarter
- Marion
- 20.0%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Marion County
Starts at Marion County's median, 1.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.9 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. Marion County's median reported result, 2017.
The data
Marion County, At a glance
Marion County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Marion 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 Marion County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 25.0% |
| 2015 | 50.0% |
| 2017 | 20.0% |
2017: 20.0%. Across these years the share ran from 20.0% to 50.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 45 tests reported to CDC for Marion 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).
Marion County, Compared
Marion County radon figures, compared
Calculated by Radon411Marion County's 45 reported tests in 2017 had a middle value of 1.9 pCi/L and a maximum of 8.1 pCi/L, and 20.0% reached 4 pCi/L. Illinois as a whole (93 Illinois counties, pooled) comes to 33.7%: 13.7 points higher than here.
Among its state's counties it ranks 65th of 70 Illinois counties with 30 or more tests for the same period. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).
Below the action level, 24 tests (53.3%) came in under 2 pCi/L, against 37.7% statewide, and 12 tests (26.7%) fell between 2 and 4, against 28.6% statewide. The busiest year on file was 2014, with 72 tests reported; the quietest, 2015, had 24.
EPA's 1993 zone map puts Marion 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 11.8% in Washington County to 37.6% in Clinton County, with Jefferson County and Washington County below Marion County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Marion County, Geology
The ground under Marion County
PredictedUSGS's geologic map puts all of Marion 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.
Marion County beside the ground around it
Across Illinois 64.5% of the land is rated high; none of Marion County's is. Of the 6 counties that border it, none has as large a share of moderate-potential ground; Clay County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Marion County, Local resources
Radon testing and mitigation in Marion 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
Marion County, Questions
Questions about radon in Marion County
Are radon levels high in Marion County?
In 2017, 20.0% of the radon tests reported to CDC for Marion County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 64 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Marion County?
Marion County borders 6 counties: Fayette County, Jefferson County, Clay County, Clinton County, Wayne County and Washington County.
Products
Marion County, Products
Testing a home in Marion County
In Marion County, 20.0% of 45 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 Marion 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
MonitorAEGTEST
HOUND-3786 rechargeable radon monitor with a 3.5-inch color screen
- C-NRPP 2024/25: Not included
- Battery
- 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
Marion County, Bordering counties
Counties bordering Marion County
Calculated by Radon411- Radon levels in Clinton CountyEPA zone 2
37.6%at or above 4 pCi/L
Median 3.0 pCi/L · 582 tests · 17.6 points above Marion County
- Radon levels in Fayette CountyEPA zone 2
26.3%at or above 4 pCi/L
Median 2.5 pCi/L · 57 tests · 6.3 points above Marion County
- Radon levels in Jefferson CountyEPA zone 2
19.6%at or above 4 pCi/L
Median 1.9 pCi/L · 138 tests · 0.4 points below Marion County
- Radon levels in Washington CountyEPA zone 2
11.8%at or above 4 pCi/L
Median 2.0 pCi/L · 51 tests · 8.2 points below Marion County
- Radon levels in Wayne CountyEPA zone 2
0.0%at or above 4 pCi/L
Median 1.6 pCi/L · 6 tests · 20.0 points below Marion County
- Radon levels in Clay CountyEPA zone 2
No CDC figure for 2017; its page reads it against its own neighbours.
Marion County, Cities and towns
Cities and towns in Marion County
About 36,382 people live in Marion County by the Census Bureau's estimate for July 1, 2025, 1,274 fewer than in 2020 (−3.4%). That works out to 64 people per square mile of land. Centralia, the largest place on its list (11,863 residents in all), extends beyond Marion County, so no share of the total is worked out for it. Reported testing is thin here: 45 tests over 2017, or 1.2 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Centralia to Walnut Hill, CDC publishes no figure by town: each reads Marion County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Centraliaextends beyond Marion County | 11,863 | −2.1% | Counted whole |
| Salem | 7,035 | −3.3% | 19.3% |
| Sandoval | 1,123 | −3.3% | 3.1% |
| Central City | 1,067 | −3.3% | 2.9% |
| Wamacextends beyond Marion County | 962 | −2.2% | Counted whole |
| Odin | 903 | −3.5% | 2.5% |
| Kinmundy | 702 | −3.4% | 1.9% |
| Farinaextends beyond Marion County | 524 | −2.6% | Counted whole |
| Junction City | 517 | −2.8% | 1.4% |
| Patoka | 507 | −4.2% | 1.4% |
| Iuka | 491 | −3.2% | 1.3% |
| Alma | 302 | −2.9% | 0.8% |
- Kell
- Vernon
- Walnut Hill
15 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Marion County is counted whole, so it has no share.
Marion County, Homes
Homes in Marion County
Of Marion County's 17,379 homes, 71% are detached houses, against 58% across Illinois; 17% are mobile homes. Half of its homes were built before 1973, close to Illinois' 1970: 34% date from before 1960 and 15% from 2000 or later. 74% of occupied homes are lived in by their owner (Illinois: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Marion County | Illinois |
|---|---|---|
| Housing units | 17,379 | 5,443,501 |
| Detached houses | 71% | 58% |
| In buildings of 5 or more | 6% | 22% |
| Mobile homes | 17% | 2% |
| Built before 1960 | 34% | 38% |
| Built since 2000 | 15% | 16% |
| Middle year built | 1973 | 1970 |
| Owner-occupied | 74% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.