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Radon Levels in Darke County, Ohio

EPA puts Darke County in Zone 1, its highest radon zone, and high results are common there: 63.7% of the 270 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

    63.7%

    11.4 pts above OH

    Darke
    63.7%
    Ohio
    52.3%

    270 tests, 2008 to 2017

  • Median result

    5.6pCi/L

    Action level reached

    Darke
    5.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    270

    50th of 79 by tests

    Darke
    270
    Franklin
    16,142

    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 Ohio

    17 of 79

    Top quarter

    Darke
    63.7%
    Pickaway
    81.4%

    By share, of 79 with 30+ tests

Read a result for Darke County

Starts at Darke County's median, 5.6 pCi/L

5.6pCi/L

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

EPA’s reading of 5.6 pCi/L

At or above 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 at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Darke County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Darke County, At a glance

Darke County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Darke 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Darke County, 2008 to 2017, laboratory
Under 2 pCi/L: 14%2 to 4 pCi/L: 22%4 pCi/L and above: 64%

Of 270 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Darke County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L3914.4%
2 to 4 pCi/L5921.9%
4 pCi/L and above17263.7%
What these figures count

These are the 270 tests reported to CDC for Darke 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

Darke County, Compared

Darke County radon figures, compared

Calculated by Radon411

More than half: 63.7% of the 270 radon tests reported to CDC for Darke County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 17th of 79 Ohio counties with 30 or more tests for the same period. That is 11.4 points above the 52.3% pooled from 88 Ohio counties.

The median result, 5.6 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 44.7 pCi/L. The rest split 14.4% under 2 pCi/L and 21.9% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 63.7% share point the same way here.

2 of its 7 bordering counties with figures ran higher, led by Auglaize County at 71.2%; Montgomery County reported 50.3%. Statewide for the same period, Pickaway County reported the highest share (81.4%) and Cuyahoga County the lowest (21.7%).

CDC's ten-year totals for Darke County went from 544 tests (2005 to 2014) to 270 (2008 to 2017), the share going from 56.4% to 63.7%.

Nationally, every county with a figure for the same period pools to 35.7%; Darke County sits 28.0 points above it. CDC also counts 11 tests taken after mitigation in Darke County for the same period: tests in homes where a fix was already in.

Darke County against Ohio, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Darke County
Darke County27063.7%5.6 pCi/LThis county
Ohio, pooled88 counties, pooled98,84052.3%Not pooled−11.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−28.0 points
Pickaway Countyhighest in the state18381.4%9.5 pCi/L+17.7 points
Cuyahoga Countylowest in the state10,09221.7%2.0 pCi/L−42.0 points
Auglaize County, OHborders it13971.2%6.5 pCi/L+7.5 points
Miami County, OHborders it69065.2%6.1 pCi/L+1.5 points
Preble County, OHborders it21262.7%5.5 pCi/L−1.0 points
Randolph County, INborders it2860.7%4.5 pCi/L−3.0 points
Shelby County, OHborders it24860.1%5.2 pCi/L−3.6 points
Mercer County, OHborders it14957.7%5.1 pCi/L−6.0 points
Wayne County, INborders it14056.4%4.5 pCi/L−7.3 points
Montgomery County, OHborders it2,92250.3%4.0 pCi/L−13.4 points
Jay County, INborders it944.4%2.7 pCi/L−19.3 points
Where Darke County's reported results fell, 2008 to 2017, laboratory, beside Ohio and the United States
ResultDarke County testsDarke County shareOhio shareU.S. shareAgainst Ohio
Under 2 pCi/L3914.4%23.1%39.6%−8.7 points
2 to 4 pCi/L5921.9%24.6%24.7%−2.7 points
4 pCi/L and above17263.7%52.3%35.7%+11.4 points
Darke County ranked among the 79 Ohio counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Tuscarawas County12 of 7954766.4%5.6 pCi/L
Marion County13 of 7926565.3%6.4 pCi/L
Miami County14 of 7969065.2%6.1 pCi/L
Morrow County15 of 7917765.0%5.7 pCi/L
Holmes County16 of 796764.2%5.8 pCi/L
Darke County17 of 7927063.7%5.6 pCi/L
Ashland County18 of 7934062.9%5.4 pCi/L
Preble County19 of 7921262.7%5.5 pCi/L
Richland County20 of 791,32762.2%5.2 pCi/L
Wayne County21 of 791,07461.8%4.9 pCi/L
Henry County22 of 793461.8%5.3 pCi/L
Darke County ten-year laboratory totals, against Ohio's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestOhio, pooledChange from the row before
2008 to 201727063.7%5.6 pCi/L44.7 pCi/L52.3%+3.3 points
2007 to 201632360.4%4.8 pCi/L44.7 pCi/L52.8%+3.4 points
2006 to 201543057.0%4.5 pCi/L47.6 pCi/L52.9%+0.6 points
2005 to 201454456.4%4.6 pCi/L84.5 pCi/L52.4%First on file

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

Darke County, Geology

The ground under Darke County

Predicted

USGS's geologic map puts all of Darke County's mapped land in one class: high radon potential. All of it lies in the area the map calls Till Plains, to which USGS gives a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Darke County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Till PlainsGlacial deposits underlain by Ordovician through Devonian limestone and shale.High14100%

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

Darke County beside the ground around it

Darke County has more high-potential ground than Ohio as a whole: 100% of its land against 62.8%. Of the 9 counties that border it, none has as large a share of high-potential ground; Auglaize County comes nearest at 100%.

Share of land by USGS radon potential: Darke County, the 9 counties bordering it and Ohio
AreaEPA zoneLow potentialModerate potentialHigh potential
Darke CountyZone 1NoneNone100%
Mercer CountyZone 1NoneNone100%
Miami CountyZone 1NoneNone100%
Randolph County, INZone 1NoneNone100%
Preble CountyZone 1NoneNone100%
Shelby CountyZone 1NoneNone100%
Jay County, INZone 1NoneNone100%
Wayne County, INZone 1NoneNone100%
Auglaize CountyZone 1NoneNone100%
Montgomery CountyZone 1NoneNone100%
Ohio88 counties, pooled by land areaVariesNone37.2%62.8%

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

Local help

Darke County, Local resources

Radon testing and mitigation in Darke County

Listed radon businesses with an address in Darke County:

Listed radon professionals by town: Arcanum, New Madison

What Ohio's program says
Phone
614-728-0272
Email
indoor.radon@odh.ohio.gov
Licensing of radon professionals
This program licenses companies and persons directly involved with the radon testing and mitigation industry.

What it means

Darke County, Questions

Questions about radon in Darke County

Are radon levels high in Darke County?

Over the 2008 to 2017 laboratory totals, 63.7% of the radon tests reported to CDC for Darke County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.6 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 16 reported a higher share; pooled, the state comes to 52.3%.

Which counties border Darke County?

Darke County borders 9 counties: Mercer County, OH, Miami County, OH, Randolph County, IN, Preble County, OH, Shelby County, OH, Jay County, IN, Wayne County, IN, Auglaize County, OH and Montgomery County, OH.

Products

Darke County, Products

Testing a home in Darke County

In Darke County, 63.7% of 270 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 52.3% pooled across Ohio. In Zone 1 the year-round level in Darke 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

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

Explore

Darke County, Bordering counties

Counties bordering Darke County

Calculated by Radon411

Darke County, Cities and towns

Cities and towns in Darke County

About 51,520 people live in Darke County by the Census Bureau's estimate for July 1, 2025, 381 fewer than in 2020 (−0.7%). That works out to 86 people per square mile of land. Its largest town, Greenville, has 12,680 residents, 24.6% of the total. Reported testing is thin here: 270 tests over 2008 to 2017, or 5.2 for every 1,000 residents (2025 estimate), where Ohio as a whole comes to 8.3.

From Greenville to Ithaca, CDC publishes no figure by town: each reads Darke County's.

The 12 largest cities and towns in Darke County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Greenville12,680−1.0%24.6%
Versailles2,723−0.7%5.3%
Arcanum2,327−0.7%4.5%
Bradfordextends beyond Darke County1,814+1.1%Counted whole
Union City1,567−0.7%3.0%
Ansonia1,147−0.4%2.2%
New Madison831−1.2%1.6%
Wayne Lakes685−0.6%1.3%
Gettysburg463−0.6%0.9%
Pitsburg377−1.3%0.7%
Osgood302−1.9%0.6%
Burkettsvilleextends beyond Darke County266−1.8%Counted whole
  • Hollansburg
  • Gordon
  • North Star
  • Palestine
  • Rossburg
  • New Weston
  • Yorkshire
  • Castine
  • Ithaca

21 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 Darke County is counted whole, so it has no share.

Darke County, Homes

Homes in Darke County

Darke County is a place of houses on their own lots: 82% of its 22,643 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1963, close to Ohio's 1970: 47% date from before 1960 and 9% from 2000 or later. 72% of occupied homes are lived in by their owner (Ohio: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Darke County, Ohio, 2019 to 2023
HomesDarke CountyOhio
Housing units22,6435,271,573
Detached houses82%69%
In buildings of 5 or more4%15%
Mobile homes4%4%
Built before 196047%38%
Built since 20009%16%
Middle year built19631970
Owner-occupied72%67%

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