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
Locations and reports
Radon Levels in Marion County, Kentucky
EPA puts Marion County in Zone 1, its highest radon zone, and high results are common there: 48.6% of the 177 radon tests reported to CDC (2008 to 2017, laboratory totals) came back 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
48.6%
4.9 pts above KY
- Marion
- 48.6%
- Kentucky
- 43.7%
177 tests, 2008 to 2017
Median result
3.9pCi/L
Below action level
- Marion
- 3.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
177
23rd of 69 by tests
- Marion
- 177
- Jefferson
- 6,590
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Kentucky
17 of 69
Top quarter
- Marion
- 48.6%
- Meade
- 68.4%
By share, of 69 with 30+ tests
Read a result for Marion County
Starts at Marion County's median, 3.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.9 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. 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 1: highest predicted potential
EPA puts all of Marion County in
USGS geologic potential: High across 68% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Marion County, 2008 to 2017, laboratory
Under 2 pCi/L: 30%2 to 4 pCi/L: 21%4 pCi/L and above: 49%
Of 177 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 54 | 30.5% |
| 2 to 4 pCi/L | 37 | 20.9% |
| 4 pCi/L and above | 86 | 48.6% |
What these figures count
These are the 177 tests reported to CDC for Marion County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Marion County, Compared
Marion County radon figures, compared
Calculated by Radon411In Marion County, about 5 in 10 reported tests over the 2008 to 2017 laboratory totals (86 of 177) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 12.9 points higher. Across 120 Kentucky counties pooled together, 43.7% of tests reached that level, so Marion County runs 4.9 points above its state.
Of 6 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 27.3% (Washington County) to 66.1% (Nelson County). By share, Marion County is 17th of 69 Kentucky counties with 30 or more tests for the same period.
Half the tests came in under 3.9 pCi/L and half over it; the single highest reached 122.3 pCi/L. Below the action level, 54 tests (30.5%) came in under 2 pCi/L, against 33.2% statewide, and 37 tests (20.9%) fell between 2 and 4, against 23.1% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 48.6% share point the same way here. USGS geology rates 68% of the county's land high radon potential. CDC also counts 11 tests taken after mitigation in Marion County for the same period: tests in homes where a fix was already in.
CDC's ten-year totals for Marion County went from 164 tests (2005 to 2014) to 177 (2008 to 2017), the share going from 55.5% to 48.6%.
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 splits Marion County: 67.7% of its land is high radon potential and 32.3% moderate. The map puts 60.5% of Marion County in the area it calls New Albany-Chattanooga Shale and 27.4% in Outer Bluegrass, with 2 smaller areas beside them. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| New Albany-Chattanooga Shale | Devonian/Mississippian Black shale. | High | 14 | 60.5% |
| Outer Bluegrass | Ordovician-Devonian limestone and shale. | Moderate | 11 | 27.4% |
| Eastern Pennyroyal | Marine shale, sandstone and limestone. | High | 12 | 7.3% |
| Mississippian Plateau | Mississippian marine limestones, dolomites, marine sandstones, siltstones, and shales. | Moderate | 11 | 4.9% |
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
Marion County has more high-potential ground than Kentucky as a whole: 67.7% of its land against 18.2%. Of the 6 counties that border it, 2 have more high-potential ground, Casey County the most 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
- Kentucky's radon programKentucky Board of Radon SafetyKentucky's radon program answers questions about testing, mitigation and the rules in Kentucky.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 Kentucky8 professionals are listed in Kentucky.
What Kentucky's program says
- Phone
- 502-782-2782
- Radon@ky.gov
What it means
Marion County, Questions
Questions about radon in Marion County
Are radon levels high in Marion County?
Over the 2008 to 2017 laboratory totals, 48.6% of the radon tests reported to CDC for Marion County, Kentucky were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.9 pCi/L. Of 69 Kentucky counties with 30 or more tests for the same period, 16 reported a higher share; pooled, the state comes to 43.7%.
Which counties border Marion County?
Marion County borders 6 counties: Washington County, Taylor County, Nelson County, Boyle County, Larue County and Casey County.
Products
Marion County, Products
Testing a home in Marion County
In Marion County, 48.6% of 177 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 43.7% pooled across Kentucky. In Zone 1 the year-round level in Marion County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
Monitor
RadonPro Wi-Fi radon monitor with a built-in Geiger counter
- C-NRPP 2024/25: Not included
- Plug-in
- Wi-Fi
- Alarm
- Screen, app
First reading: Within 5 minutes
Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Marion County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Marion County
Explore
Marion County, Bordering counties
Counties bordering Marion County
Calculated by Radon411- Radon levels in Nelson CountyEPA zone 1
66.1%at or above 4 pCi/L
Median 6.3 pCi/L · 304 tests · 17.5 points above Marion County
- Radon levels in Taylor CountyEPA zone 1
57.1%at or above 4 pCi/L
Median 4.4 pCi/L · 91 tests · 8.5 points above Marion County
- Radon levels in Boyle CountyEPA zone 1
53.9%at or above 4 pCi/L
Median 4.4 pCi/L · 492 tests · 5.3 points above Marion County
- Radon levels in Larue CountyEPA zone 2
47.1%at or above 4 pCi/L
Median 3.7 pCi/L · 34 tests · 1.5 points below Marion County
- Radon levels in Casey CountyEPA zone 1
32.6%at or above 4 pCi/L
Median 3.1 pCi/L · 43 tests · 16.0 points below Marion County
- Radon levels in Washington CountyEPA zone 2
27.3%at or above 4 pCi/L
Median 2.4 pCi/L · 44 tests · 21.3 points below Marion County
Marion County, Cities and towns
Cities and towns in Marion County
The Census Bureau estimates 20,115 residents in Marion County for July 1, 2025, 528 more than in 2020 (+2.7%). That works out to 59 people per square mile of land. Its largest town, Lebanon, has 6,699 residents, 33.3% of the total. Together its 5 incorporated places hold 39.7% of those residents; the other 60.3% live outside any of them. CDC's 177 reported tests for 2008 to 2017 work out to 8.8 per 1,000 residents (2025 estimate), close to Kentucky's 6.3.
From Lebanon to St. Mary, CDC publishes no figure by town: each reads Marion County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Lebanon | 6,699 | +6.4% | 33.3% |
| Loretto | 714 | −0.3% | 3.5% |
| Bradfordsville | 283 | +3.7% | 1.4% |
| Raywick | 155 | +0.6% | 0.8% |
| St. Mary | 138 | −0.7% | 0.7% |
5 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).
Marion County, Homes
Homes in Marion County
Marion County is a place of houses on their own lots: 75% of its 8,427 homes are detached single-family houses, against 68% across Kentucky. Half of its homes were built before 1982, close to Kentucky's 1982: 22% date from before 1960 and 24% from 2000 or later. Owners live in 77% of the occupied homes (Kentucky: 68%), so for most households a test and a fix are their own to order.
| Homes | Marion County | Kentucky |
|---|---|---|
| Housing units | 8,427 | 2,010,655 |
| Detached houses | 75% | 68% |
| In buildings of 5 or more | 5% | 12% |
| Mobile homes | 14% | 11% |
| Built before 1960 | 22% | 22% |
| Built since 2000 | 24% | 24% |
| Middle year built | 1982 | 1982 |
| Owner-occupied | 77% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.