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Radon Levels in Clark County, Indiana

EPA puts Clark County in Zone 1, its highest radon zone, and high results are common there: 47.7% of the 512 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    47.7%

    8.8 pts above IN

    Clark
    47.7%
    Indiana
    38.9%

    512 tests, 2008 to 2017

  • Median result

    3.6pCi/L

    Below action level

    Clark
    3.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    512

    18th of 69 by tests

    Clark
    512
    St. Joseph
    7,346

    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 Indiana

    24 of 69

    Middle half

    Clark
    47.7%
    Miami
    63.3%

    By share, of 69 with 30+ tests

Read a result for Clark County

Starts at Clark County's median, 3.6 pCi/L

3.6pCi/L

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

EPA’s reading of 3.6 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: High across 51% 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: 31%2 to 4 pCi/L: 21%4 pCi/L and above: 48%

Of 512 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/L16131.4%
2 to 4 pCi/L10720.9%
4 pCi/L and above24447.7%
What these figures count

These are the 512 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

In Clark County, about 5 in 10 reported tests over the 2008 to 2017 laboratory totals (244 of 512) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 12.0 points higher. Across 92 Indiana counties pooled together, 38.9% of tests reached that level, so Clark County runs 8.8 points above its state.

Of 5 neighbours with a figure, none reported a larger share at or above 4 pCi/L; the spread is 37.1% (Oldham County, KY) to 45.8% (Jefferson County). By share, Clark County is 24th of 69 Indiana counties with 30 or more tests for the same period.

Half the tests came in under 3.6 pCi/L and half over it; the single highest reached 146.3 pCi/L. Below the action level, 161 tests (31.4%) came in under 2 pCi/L, against 32.8% statewide, and 107 tests (20.9%) fell between 2 and 4, against 28.3% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 47.7% share point the same way here. USGS geology rates 51% of the county's land high radon potential. CDC also counts 45 tests taken after mitigation in Clark County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Clark County went from 376 tests (2005 to 2014) to 512 (2008 to 2017), the share going from 53.5% to 47.7%.

Clark County against Indiana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Clark County
Clark County51247.7%3.6 pCi/LThis county
Indiana, pooled92 counties, pooled43,14838.9%Not pooled−8.8 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−12.0 points
Miami Countyhighest in the state3063.3%5.3 pCi/L+15.6 points
Jasper Countylowest in the state7114.1%1.2 pCi/L−33.6 points
Jefferson County, INborders it7245.8%3.1 pCi/L−1.9 points
Trimble County, KYborders it2445.8%3.7 pCi/L−1.9 points
Floyd County, INborders it31642.4%3.3 pCi/L−5.3 points
Washington County, INborders it3842.1%3.5 pCi/L−5.6 points
Jefferson County, KYborders it6,59039.4%2.7 pCi/L−8.3 points
Oldham County, KYborders it80337.1%2.7 pCi/L−10.6 points
Scott County, INborders it1735.3%2.0 pCi/L−12.4 points
Where Clark County's reported results fell, 2008 to 2017, laboratory, beside Indiana and the United States
ResultClark County testsClark County shareIndiana shareU.S. shareAgainst Indiana
Under 2 pCi/L16131.4%32.8%39.6%−1.4 points
2 to 4 pCi/L10720.9%28.3%24.7%−7.4 points
4 pCi/L and above24447.7%38.9%35.7%+8.8 points
Clark County ranked among the 69 Indiana counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Howard County19 of 6921649.1%3.8 pCi/L
Madison County20 of 6923949.0%3.8 pCi/L
Bartholomew County21 of 691,70748.7%3.9 pCi/L
Adams County22 of 696648.5%3.8 pCi/L
Wells County23 of 6916147.8%3.6 pCi/L
Clark County24 of 6951247.7%3.6 pCi/L
Porter County25 of 691,13646.5%3.5 pCi/L
Fulton County26 of 699746.4%3.3 pCi/L
Elkhart County27 of 692,85646.4%3.7 pCi/L
Clinton County28 of 698545.9%3.5 pCi/L
Jefferson County29 of 697245.8%3.1 pCi/L
Clark County ten-year laboratory totals, against Indiana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIndiana, pooledChange from the row before
2008 to 201751247.7%3.6 pCi/L146.3 pCi/L38.9%−3.2 points
2007 to 201648950.9%4.0 pCi/L146.3 pCi/L39.2%−0.4 points
2006 to 201545251.3%4.0 pCi/L146.3 pCi/L39.6%−2.2 points
2005 to 201437653.5%4.5 pCi/L146.3 pCi/L39.3%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: 50.9% of its land is high radon potential and 49.1% moderate. The map puts 50.7% of Clark County in the area it calls New Albany Shale and 29.6% in Crawford Upland/Mitchell Plain/Norman Upland, with one smaller area beside them. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Clark County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
New Albany ShaleNew Albany black shale.High1250.7%
Crawford Upland/Mitchell Plain/Norman UplandUnglaciated, underlain by karsted Mississippian carbonate rocks.Moderate1129.6%
Dearborn UplandOrdovician through Devonian limestone, dolostone, and gray shale, and pre-Wisconsinan glacial deposits.Moderate1019.5%

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 Indiana as a whole: 50.9% of its land against 56.6%. Of the 7 counties that border it, 3 have more high-potential ground, Scott County the most at 61.6%.

Share of land by USGS radon potential: Clark County, the 7 counties bordering it and Indiana
AreaEPA zoneLow potentialModerate potentialHigh potential
Clark CountyZone 1None49.1%50.9%
Floyd CountyZone 2None95.7%4.3%
Oldham County, KYZone 2None48.3%51.7%
Jefferson County, KYZone 1None44.9%55.1%
Scott CountyZone 1None38.4%61.6%
Washington CountyZone 1None100%None
Trimble County, KYZone 2None100%None
Jefferson CountyZone 2None76.2%23.8%
Indiana92 counties, pooled by land areaVariesNone43.4%56.6%

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 Indiana's program says
Phone
1-800-272-9723
Licensing of radon professionals
According to the Indiana Radon Rule, 410 IAC 5.1, everyone who is serving Indiana by doing radon testing, analysis and mitigation (radon reduction) in residential structures must be certified by the Indiana State Department of Health.

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, 47.7% of the radon tests reported to CDC for Clark County, Indiana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.6 pCi/L. Of 69 Indiana counties with 30 or more tests for the same period, 23 reported a higher share; pooled, the state comes to 38.9%.

Which counties border Clark County?

Clark County borders 7 counties: Floyd County, IN, Oldham County, KY, Jefferson County, KY, Scott County, IN, Washington County, IN, Trimble County, KY and Jefferson County, IN.

Products

Clark County, Products

Testing a home in Clark County

In Clark County, 47.7% of 512 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 38.9% pooled across Indiana. 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

Clark County is growing: the Census Bureau puts it at 130,451 residents on July 1, 2025, up 7.5% from 121,374 in 2020. That works out to 350 people per square mile of land. Its largest town, Jeffersonville, has 54,134 residents, 41.5% of the total. Together its 6 incorporated places hold 74.8% of those residents; the other 25.2% live outside any of them. Reported testing is thin here: 512 tests over 2008 to 2017, or 3.9 for every 1,000 residents (2025 estimate), where Indiana as a whole comes to 6.2.

From Jeffersonville to Borden, CDC publishes no figure by town: each reads Clark County's.

The cities and towns in Clark County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Jeffersonville54,134+9.2%41.5%
Clarksville22,253−0.3%17.1%
Sellersburg10,305+9.9%7.9%
Charlestown8,802+12.1%6.7%
Utica1,298+45.0%1.0%
Borden842+7.3%0.6%

6 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).

Clark County, Homes

Homes in Clark County

Of Clark County's 53,854 homes, 73% are detached houses, against 73% across Indiana; 13% are in buildings of five or more homes. Half of its homes were built before 1981, close to Indiana's 1976: 22% date from before 1960 and 29% from 2000 or later. 75% of occupied homes are lived in by their owner (Indiana: 70%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Clark County, Indiana, 2019 to 2023
HomesClark CountyIndiana
Housing units53,8542,953,344
Detached houses73%73%
In buildings of 5 or more13%13%
Mobile homes5%4%
Built before 196022%32%
Built since 200029%21%
Middle year built19811976
Owner-occupied75%70%

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