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Radon Levels in Clark County, Kentucky

EPA puts Clark County in Zone 1, its highest radon zone, and 29.0% of its 231 reported radon tests (2008 to 2017, laboratory totals) 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

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  • Share at 4+ pCi/L

    29.0%

    14.7 pts below KY

    Clark
    29.0%
    Kentucky
    43.7%

    231 tests, 2008 to 2017

  • Median result

    2.4pCi/L

    Below action level

    Clark
    2.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    231

    20th of 69 by tests

    Clark
    231
    Jefferson
    6,590

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Kentucky

    47 of 69

    Middle half

    Clark
    29.0%
    Meade
    68.4%

    By share, of 69 with 30+ tests

Read a result for Clark County

Starts at Clark County's median, 2.4 pCi/L

2.4pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 2.4 pCi/L

Between 2 and 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Clark County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Clark County, At a glance

Clark County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Clark County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: Moderate across 73% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Clark County, 2008 to 2017, laboratory

Reported results by concentration band, Clark County, 2008 to 2017, laboratory
Under 2 pCi/L: 43%2 to 4 pCi/L: 28%4 pCi/L and above: 29%

Of 231 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Clark County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L9942.9%
2 to 4 pCi/L6528.1%
4 pCi/L and above6729.0%
What these figures count

These are the 231 tests reported to CDC for Clark 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).

How to read these figures

Clark County, Compared

Clark County radon figures, compared

Calculated by Radon411

Clark County's 231 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.4 pCi/L and a maximum of 61.5 pCi/L, and 29.0% reached 4 pCi/L. Kentucky as a whole (120 Kentucky counties, pooled) comes to 43.7%: 14.7 points higher than here.

Among its state's counties it ranks 47th of 69 Kentucky counties with 30 or more tests for the same period. Statewide for the same period, Meade County reported the highest share (68.4%) and Hopkins County the lowest (9.5%).

Below the action level, 99 tests (42.9%) came in under 2 pCi/L, against 33.2% statewide, and 65 tests (28.1%) fell between 2 and 4, against 23.1% statewide. CDC's ten-year totals for Clark County went from 157 tests (2005 to 2014) to 231 (2008 to 2017), the share going from 31.2% to 29.0%.

EPA's 1993 zone map puts Clark County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 73% of the county's land moderate radon potential.

Next door, the shares run from 38.7% in Madison County to 54.5% in Fayette County.

CDC also counts 7 tests taken after mitigation in Clark County for the same period: tests in homes where a fix was already in.

Clark County against Kentucky, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Clark County
Clark County23129.0%2.4 pCi/LThis county
Kentucky, pooled120 counties, pooled28,79343.7%Not pooled+14.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+6.7 points
Meade Countyhighest in the state11768.4%8.2 pCi/L+39.4 points
Hopkins Countylowest in the state429.5%1.7 pCi/L−19.5 points
Fayette County, KYborders it5,26354.5%4.5 pCi/L+25.5 points
Bourbon County, KYborders it12753.5%4.8 pCi/L+24.5 points
Montgomery County, KYborders it10551.4%4.1 pCi/L+22.4 points
Powell County, KYborders it2944.8%3.2 pCi/L+15.8 points
Estill County, KYborders it17744.1%3.2 pCi/L+15.1 points
Madison County, KYborders it60438.7%2.9 pCi/L+9.7 points
Where Clark County's reported results fell, 2008 to 2017, laboratory, beside Kentucky and the United States
ResultClark County testsClark County shareKentucky shareU.S. shareAgainst Kentucky
Under 2 pCi/L9942.9%33.2%39.6%+9.7 points
2 to 4 pCi/L6528.1%23.1%24.7%+5.0 points
4 pCi/L and above6729.0%43.7%35.7%−14.7 points
Clark County ranked among the 69 Kentucky counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Carter County42 of 694131.7%2.2 pCi/L
Logan County43 of 697931.6%2.4 pCi/L
Spencer County44 of 6916631.3%2.5 pCi/L
Breckinridge County45 of 693231.3%2.5 pCi/L
Allen County46 of 695829.3%1.9 pCi/L
Clark County47 of 6923129.0%2.4 pCi/L
Grayson County48 of 693627.8%2.2 pCi/L
Washington County49 of 694427.3%2.4 pCi/L
Pendleton County50 of 693426.5%1.9 pCi/L
Campbell County51 of 6954326.2%2.3 pCi/L
Kenton County52 of 691,16726.0%2.3 pCi/L
Clark County ten-year laboratory totals, against Kentucky's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestKentucky, pooledChange from the row before
2008 to 201723129.0%2.4 pCi/L61.5 pCi/L43.7%−1.3 points
2007 to 201621130.3%2.5 pCi/L61.5 pCi/L45.1%−1.0 points
2006 to 201519231.3%2.4 pCi/L41.6 pCi/L46.4%+0.1 points
2005 to 201415731.2%2.4 pCi/L31.0 pCi/L47.3%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Clark County, Geology

The ground under Clark County

Predicted

USGS's geologic map splits Clark County: 73.0% of its land is moderate radon potential and 27.0% high. The map puts 73.0% of Clark County in the area it calls Outer Bluegrass and 16.0% in New Albany-Chattanooga Shale, with one smaller area beside them. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 14, in the high band (12 to 17).

USGS's geologic areas under Clark County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Outer BluegrassOrdovician-Devonian limestone and shale.Moderate1173.0%
New Albany-Chattanooga ShaleDevonian/Mississippian Black shale.High1416.0%
Inner BluegrassOrdovician limestones, dolomites and shales.High1310.9%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Clark County beside the ground around it

On high-potential ground Clark County is close to Kentucky as a whole: 27.0% of its land against 18.2%. Of the 6 counties that border it, 5 have more high-potential ground, Fayette County the most at 76.8%.

Share of land by USGS radon potential: Clark County, the 6 counties bordering it and Kentucky
AreaEPA zoneLow potentialModerate potentialHigh potential
Clark CountyZone 1None73.0%27.0%
Montgomery CountyZone 2None61.3%38.7%
Fayette CountyZone 1None23.2%76.8%
Bourbon CountyZone 1None55.9%44.1%
Madison CountyZone 2None61.3%38.7%
Powell CountyZone 2None75.6%24.4%
Estill CountyZone 2None57.3%42.7%
Kentucky120 counties, pooled by land areaVaries5.7%76.1%18.2%

The map rates the ground, not the air in any home.

Local help

Clark County, Local resources

Radon testing and mitigation in Clark County

What Kentucky's program says
Phone
502-782-2782
Email
Radon@ky.gov

What it means

Clark County, Questions

Questions about radon in Clark County

Are radon levels high in Clark County?

Over the 2008 to 2017 laboratory totals, 29.0% of the radon tests reported to CDC for Clark County, Kentucky were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.4 pCi/L. Of 69 Kentucky counties with 30 or more tests for the same period, 46 reported a higher share; pooled, the state comes to 43.7%.

Which counties border Clark County?

Clark County borders 6 counties: Montgomery County, Fayette County, Bourbon County, Madison County, Powell County and Estill County.

Products

Clark County, Products

Testing a home in Clark County

In Clark County, 29.0% of 231 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 Clark 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

Clark County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Clark County

Explore

Clark County, Bordering counties

Counties bordering Clark County

Calculated by Radon411

Clark County, Cities and towns

Cities and towns in Clark County

The Census Bureau estimates 37,888 residents in Clark County for July 1, 2025, 855 more than in 2020 (+2.3%). That works out to 150 people per square mile of land. Winchester, its one incorporated place, has 19,514 residents, 51.5% of the total. CDC's 231 reported tests for 2008 to 2017 work out to 6.1 per 1,000 residents (2025 estimate), close to Kentucky's 6.3.

Winchester is the one incorporated place here; CDC publishes no figure by town, so it reads Clark County's.

Winchester, Clark County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Winchester19,514+1.8%51.5%

One incorporated place, 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).

Clark County, Homes

Homes in Clark County

Of Clark County's 16,279 homes, 71% are detached houses, against 68% across Kentucky; 8% are in buildings of five or more homes. Half of its homes were built before 1979, close to Kentucky's 1982: 24% date from before 1960 and 21% from 2000 or later. 71% of occupied homes are lived in by their owner (Kentucky: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Clark County, Kentucky, 2019 to 2023
HomesClark CountyKentucky
Housing units16,2792,010,655
Detached houses71%68%
In buildings of 5 or more8%12%
Mobile homes7%11%
Built before 196024%22%
Built since 200021%24%
Middle year built19791982
Owner-occupied71%68%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.