Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
Locations and reports
Radon Levels in Marion County, Missouri
EPA puts Marion 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
Share at 4+ pCi/L
41.8%
11.2 pts above MO
- Marion
- 41.8%
- Missouri
- 30.6%
282 tests, 2008 to 2017
Median result
3.2pCi/L
Below action level
- Marion
- 3.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
282
18th of 72 by tests
- Marion
- 282
- St. Louis
- 17,747
Reported to CDC before any fix, 2008 to 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 Missouri
9 of 72
Top quarter
- Marion
- 41.8%
- Atchison
- 69.9%
By share, of 72 with 30+ tests
Read a result for Marion County
Starts at Marion County's median, 3.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.2 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. Marion County's median reported result, 2008 to 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 99% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Marion County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 50.0% |
| 2015 | 46.2% |
| 2016 | 27.3% |
| 2017 | 40.0% |
| 2018 | 100.0% |
| 2019 | 66.7% |
| 2020 | 0.0% |
| 2021 | 0.0% |
| 2022 | 55.6% |
| 2023 | 50.0% |
2023: 50.0%. 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 Marion 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).
Marion County, Compared
Marion County radon figures, compared
Calculated by Radon411In Marion County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (118 of 282) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 6.1 points higher. Across 115 Missouri counties pooled together, 30.6% of tests reached that level, so Marion County runs 11.2 points above its state.
The newest figure, in 2023, counts only 2 tests (50.0% at or above 4 pCi/L), too few to compare, so this reading uses the 282-test figure.
Of 5 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 23.3% (Monroe County) to 55.2% (Adams County, IL). By share, Marion County is 9th of 72 Missouri counties with 30 or more tests for the same period.
Half the tests came in under 3.2 pCi/L and half over it; the single highest reached 58.9 pCi/L. Below the action level, 80 tests (28.4%) came in under 2 pCi/L, against 41.2% statewide, and 84 tests (29.8%) fell between 2 and 4, against 28.1% statewide.
Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 41.8% share point the same way here. USGS geology rates 99% of the county's land moderate radon potential. CDC also counts 17 tests taken after mitigation in Marion County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2015, with 13 tests reported; the quietest, 2020, had 1.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Marion County, Geology
The ground under Marion County
PredictedMost of the ground under Marion County is one class on USGS's geologic map: 98.5% of its land is moderate radon potential, with 1.5% high. 98.5% of it lies in the area the map calls Dissected Till Plains, to which USGS gives a radon index of 11, in the moderate band (9 to 11).
| 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 | 98.5% |
| Galesburg Plain | Illinoian glacial deposits and loess over Paleozoic sedimentary rocks. | High | 13 | 1.5% |
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
On high-potential ground Marion County is close to Missouri as a whole: 1.5% of its land against 8.2%. Of the 6 counties that border it, 3 have more high-potential ground, Adams County, IL the most at 99.9%.
The map rates the ground, not the air in any home.
Local help
Marion County, Local resources
Radon testing and mitigation in Marion 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
Marion County, Questions
Questions about radon in Marion County
Are radon levels high in Marion County?
In 2023, 50.0% of the radon tests reported to CDC for Marion County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.3 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 8 reported a higher share; pooled, the state comes to 30.6%.
Which counties border Marion County?
Marion County borders 6 counties: Ralls County, MO, Lewis County, MO, Shelby County, MO, Adams County, IL, Monroe County, MO and Pike County, IL.
Products
Marion County, Products
Testing a home in Marion County
In Marion County, 41.8% of 282 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 30.6% pooled across Missouri. 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
MonitorKidde
Radon Detector (RAB) battery digital radon detector with an alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
- 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 Adams County, ILEPA zone 1
55.2%at or above 4 pCi/L
Median 4.5 pCi/L · 3,677 tests · 13.4 points above Marion County
- Radon levels in Pike County, ILEPA zone 1
46.3%at or above 4 pCi/L
Median 3.8 pCi/L · 108 tests · 4.5 points above Marion County
- Radon levels in Ralls County, MOEPA zone 2
32.6%at or above 4 pCi/L
Median 2.7 pCi/L · 43 tests · 9.2 points below Marion County
- Radon levels in Lewis County, MOEPA zone 2
32.4%at or above 4 pCi/L
Median 2.6 pCi/L · 71 tests · 9.4 points below Marion County
- Radon levels in Shelby County, MOEPA zone 2
24.1%at or above 4 pCi/L
Median 1.7 pCi/L · 29 tests · 17.7 points below Marion County
- Radon levels in Monroe County, MOEPA zone 2
23.3%at or above 4 pCi/L
Median 1.5 pCi/L · 30 tests · 18.5 points below Marion County
Marion County, Cities and towns
Cities and towns in Marion County
Marion County's population has barely moved since 2020: 28,525 residents on July 1, 2025 against 28,480 then, by the Census Bureau's estimates. That works out to 65 people per square mile of land. Hannibal, the largest place on its list (16,804 residents in all), extends beyond Marion County, so no share of the total is worked out for it. CDC's 282 reported tests for 2008 to 2017 work out to 9.9 per 1,000 residents (2025 estimate), close to Missouri's 9.3.
From Hannibal to Monroe City, CDC publishes no figure by town: each reads Marion County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Hannibalextends beyond Marion County | 16,804 | −1.5% | Counted whole |
| Palmyra | 3,649 | +1.2% | 12.8% |
| Monroe Cityextends beyond Marion County | 2,714 | +2.0% | Counted whole |
3 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 Marion County is counted whole, so it has no share.
Marion County, Homes
Homes in Marion County
Of Marion County's 12,886 homes, 75% are detached houses, against 70% across Missouri; 8% are in buildings of five or more homes. The homes are older than Missouri's as a whole: half were built before 1970 (1978 for Missouri), and 40% date from before 1960. 70% of occupied homes are lived in by their owner (Missouri: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Marion County | Missouri |
|---|---|---|
| Housing units | 12,886 | 2,809,501 |
| Detached houses | 75% | 70% |
| In buildings of 5 or more | 8% | 13% |
| Mobile homes | 5% | 5% |
| Built before 1960 | 40% | 28% |
| Built since 2000 | 14% | 21% |
| Middle year built | 1970 | 1978 |
| Owner-occupied | 70% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.