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Radon Levels in Defiance County, Ohio

EPA puts Defiance County in Zone 2, its middle radon zone, and high results are common there: 48.6% of the 70 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

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  • Share at 4+ pCi/L

    48.6%

    3.7 pts below OH

    Defiance
    48.6%
    Ohio
    52.3%

    70 tests, 2008 to 2017

  • Median result

    3.8pCi/L

    Below action level

    Defiance
    3.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    70

    66th of 79 by tests

    Defiance
    70
    Franklin
    16,142

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Ohio

    52 of 79

    Middle half

    Defiance
    48.6%
    Pickaway
    81.4%

    By share, of 79 with 30+ tests

Read a result for Defiance County

Starts at Defiance County's median, 3.8 pCi/L

3.8pCi/L

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

EPA’s reading of 3.8 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. Defiance County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Defiance County, At a glance

Defiance County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Defiance County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: High across 63% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Defiance County, 2008 to 2017, laboratory
Under 2 pCi/L: 23%2 to 4 pCi/L: 29%4 pCi/L and above: 48%

Of 70 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Defiance County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1622.9%
2 to 4 pCi/L2028.6%
4 pCi/L and above3448.6%
What these figures count

These are the 70 tests reported to CDC for Defiance 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

Defiance County, Compared

Defiance County radon figures, compared

Calculated by Radon411

In Defiance County, about 5 in 10 reported tests over the 2008 to 2017 laboratory totals (34 of 70) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 12.9 points higher. Across 88 Ohio counties pooled together, 52.3% of tests reached that level, so Defiance County runs 3.7 points below its state.

Of 4 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 41.8% (Allen County, IN) to 61.8% (Henry County). By share, Defiance County is 52nd of 79 Ohio counties with 30 or more tests for the same period.

Half the tests came in under 3.8 pCi/L and half over it; the single highest reached 34.4 pCi/L. Below the action level, 16 tests (22.9%) came in under 2 pCi/L, against 23.1% statewide, and 20 tests (28.6%) fell between 2 and 4, against 24.6% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 48.6% share point the same way here. USGS geology rates 63% of the county's land high radon potential. CDC also counts 8 tests taken after mitigation in Defiance County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Defiance County went from 57 tests (2005 to 2014) to 70 (2008 to 2017), the share going from 47.4% to 48.6%.

Defiance County against Ohio, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Defiance County
Defiance County7048.6%3.8 pCi/LThis county
Ohio, pooled88 counties, pooled98,84052.3%Not pooled+3.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−12.9 points
Pickaway Countyhighest in the state18381.4%9.5 pCi/L+32.8 points
Cuyahoga Countylowest in the state10,09221.7%2.0 pCi/L−26.9 points
Henry County, OHborders it3461.8%5.3 pCi/L+13.2 points
Putnam County, OHborders it9459.6%4.8 pCi/L+11.0 points
DeKalb County, INborders it24256.6%4.4 pCi/L+8.0 points
Williams County, OHborders it2842.9%3.3 pCi/L−5.7 points
Allen County, INborders it3,99041.8%3.3 pCi/L−6.8 points
Paulding County, OHborders it1323.1%3.2 pCi/L−25.5 points
Where Defiance County's reported results fell, 2008 to 2017, laboratory, beside Ohio and the United States
ResultDefiance County testsDefiance County shareOhio shareU.S. shareAgainst Ohio
Under 2 pCi/L1622.9%23.1%39.6%−0.2 points
2 to 4 pCi/L2028.6%24.6%24.7%+4.0 points
4 pCi/L and above3448.6%52.3%35.7%−3.7 points
Defiance 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
Clermont County47 of 791,36350.0%4.0 pCi/L
Harrison County48 of 794450.0%4.1 pCi/L
Jefferson County49 of 7927149.8%3.9 pCi/L
Columbiana County50 of 7966249.1%3.8 pCi/L
Perry County51 of 799048.9%3.8 pCi/L
Defiance County52 of 797048.6%3.8 pCi/L
Brown County53 of 797047.1%3.3 pCi/L
Wyandot County54 of 7932046.3%3.6 pCi/L
Hancock County55 of 791,38246.2%3.7 pCi/L
Wood County56 of 791,19245.5%3.5 pCi/L
Lorain County57 of 793,30745.4%3.6 pCi/L
Defiance County ten-year laboratory totals, against Ohio's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestOhio, pooledChange from the row before
2008 to 20177048.6%3.8 pCi/L34.4 pCi/L52.3%+3.6 points
2007 to 20166045.0%3.7 pCi/L34.4 pCi/L52.8%−1.6 points
2006 to 20155846.6%3.7 pCi/L34.4 pCi/L52.9%−0.8 points
2005 to 20145747.4%3.7 pCi/L34.4 pCi/L52.4%First on file

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

Defiance County, Geology

The ground under Defiance County

Predicted

USGS's geologic map splits Defiance County: 62.6% of its land is high radon potential and 37.4% moderate. The map puts 62.6% of Defiance County in the area it calls Till Plains and 37.4% in Lake Plains. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Defiance County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Till PlainsGlacial deposits underlain by Ordovician through Devonian limestone and shale.High1462.6%
Lake PlainsGlacial lake deposits, Devonian shale and limestone.Moderate1037.4%

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

Defiance County beside the ground around it

On high-potential ground Defiance County is close to Ohio as a whole: 62.6% of its land against 62.8%. Of the 6 counties that border it, 5 have more high-potential ground, Allen County, IN the most at 100%.

Share of land by USGS radon potential: Defiance County, the 6 counties bordering it and Ohio
AreaEPA zoneLow potentialModerate potentialHigh potential
Defiance CountyZone 2None37.4%62.6%
Williams CountyZone 2None9.7%90.3%
Paulding CountyZone 2None57.6%42.4%
Henry CountyZone 2None25.7%74.3%
DeKalb County, INZone 1NoneNone100%
Putnam CountyZone 2None32.3%67.7%
Allen County, INZone 1NoneNone100%
Ohio88 counties, pooled by land areaVariesNone37.2%62.8%

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

Local help

Defiance County, Local resources

Radon testing and mitigation in Defiance County

Listed radon businesses with an address in Defiance County:

Listed radon professionals by town: Defiance

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

Defiance County, Questions

Questions about radon in Defiance County

Are radon levels high in Defiance County?

Over the 2008 to 2017 laboratory totals, 48.6% of the radon tests reported to CDC for Defiance County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.8 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 51 reported a higher share; pooled, the state comes to 52.3%.

Which counties border Defiance County?

Defiance County borders 6 counties: Williams County, OH, Paulding County, OH, Henry County, OH, DeKalb County, IN, Putnam County, OH and Allen County, IN.

Products

Defiance County, Products

Testing a home in Defiance County

In Defiance County, 48.6% of 70 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 52.3% pooled across Ohio. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Defiance County; a long-term test tells the year-round average.

Test kits and monitors3

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Best radon monitors for Defiance County homes, compared

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Defiance County, Bordering counties

Counties bordering Defiance County

Calculated by Radon411

Defiance County, Cities and towns

Cities and towns in Defiance County

Defiance County's population has barely moved since 2020: 38,292 residents on July 1, 2025 against 38,268 then, by the Census Bureau's estimates. That works out to 93 people per square mile of land. Its largest town, Defiance, has 17,009 residents, 44.4% of the total. Together its 4 incorporated places hold 56.3% of those residents; the other 43.7% live outside any of them. Reported testing is thin here: 70 tests over 2008 to 2017, or 1.8 for every 1,000 residents (2025 estimate), where Ohio as a whole comes to 8.3.

From Defiance to Ney, CDC publishes no figure by town: each reads Defiance County's.

The cities and towns in Defiance County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Defiance17,009−0.3%44.4%
Hicksville3,427+0.1%8.9%
Sherwood816+1.7%2.1%
Ney297−1.3%0.8%

4 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).

Defiance County, Homes

Homes in Defiance County

Defiance County is a place of houses on their own lots: 81% of its 16,570 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1967, close to Ohio's 1970: 42% date from before 1960 and 11% from 2000 or later. Owners live in 79% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.

Homes in Defiance County, Ohio, 2019 to 2023
HomesDefiance CountyOhio
Housing units16,5705,271,573
Detached houses81%69%
In buildings of 5 or more5%15%
Mobile homes4%4%
Built before 196042%38%
Built since 200011%16%
Middle year built19671970
Owner-occupied79%67%

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