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Radon Levels in Highland County, Ohio

EPA puts Highland County in Zone 2, its middle radon zone, and high results are common there: 56.7% of the 67 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

    56.7%

    4.4 pts above OH

    Highland
    56.7%
    Ohio
    52.3%

    67 tests, 2008 to 2017

  • Median result

    4.8pCi/L

    Action level reached

    Highland
    4.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    67

    69th of 79 by tests

    Highland
    67
    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

    38 of 79

    Middle half

    Highland
    56.7%
    Pickaway
    81.4%

    By share, of 79 with 30+ tests

Read a result for Highland County

Starts at Highland County's median, 4.8 pCi/L

4.8pCi/L

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

EPA’s reading of 4.8 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. Highland County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Highland County, At a glance

Highland County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Highland 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: Moderate across 68% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Highland County, 2008 to 2017, laboratory
Under 2 pCi/L: 12%2 to 4 pCi/L: 31%4 pCi/L and above: 57%

Of 67 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Highland County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L811.9%
2 to 4 pCi/L2131.3%
4 pCi/L and above3856.7%
What these figures count

These are the 67 tests reported to CDC for Highland 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

Highland County, Compared

Highland County radon figures, compared

Calculated by Radon411

More than half: 56.7% of the 67 radon tests reported to CDC for Highland County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 38th of 79 Ohio counties with 30 or more tests for the same period. That is 4.4 points above the 52.3% pooled from 88 Ohio counties.

The median result, 4.8 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 30.7 pCi/L. The rest split 11.9% under 2 pCi/L and 31.3% from 2 to 4 (Ohio: 23.1% and 24.6%). The reported tests do not follow EPA's Zone 2 label for Highland County (predicted average between 2 and 4 pCi/L): 56.7% of them reached 4 pCi/L, fewer than that label suggests.

1 of its 4 bordering counties with figures ran higher, led by Ross County at 67.1%; Brown County reported 47.1%. 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 Highland County went from 59 tests (2005 to 2014) to 67 (2008 to 2017), the share going from 55.9% to 56.7%.

Nationally, every county with a figure for the same period pools to 35.7%; Highland County sits 21.0 points above it.

Highland County against Ohio, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Highland County
Highland County6756.7%4.8 pCi/LThis county
Ohio, pooled88 counties, pooled98,84052.3%Not pooled−4.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−21.0 points
Pickaway Countyhighest in the state18381.4%9.5 pCi/L+24.7 points
Cuyahoga Countylowest in the state10,09221.7%2.0 pCi/L−35.0 points
Ross County, OHborders it36867.1%7.0 pCi/L+10.4 points
Fayette County, OHborders it1258.3%5.5 pCi/L+1.6 points
Pike County, OHborders it5756.1%4.5 pCi/L−0.6 points
Clinton County, OHborders it10352.4%4.2 pCi/L−4.3 points
Adams County, OHborders it1850.0%3.8 pCi/L−6.7 points
Brown County, OHborders it7047.1%3.3 pCi/L−9.6 points
Where Highland County's reported results fell, 2008 to 2017, laboratory, beside Ohio and the United States
ResultHighland County testsHighland County shareOhio shareU.S. shareAgainst Ohio
Under 2 pCi/L811.9%23.1%39.6%−11.2 points
2 to 4 pCi/L2131.3%24.6%24.7%+6.7 points
4 pCi/L and above3856.7%52.3%35.7%+4.4 points
Highland 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
Monroe County33 of 794858.3%5.0 pCi/L
Mercer County34 of 7914957.7%5.1 pCi/L
Clark County35 of 791,44757.5%4.9 pCi/L
Carroll County36 of 7948657.4%4.8 pCi/L
Allen County37 of 7923856.7%5.0 pCi/L
Highland County38 of 796756.7%4.8 pCi/L
Muskingum County39 of 7939156.3%4.9 pCi/L
Pike County40 of 795756.1%4.5 pCi/L
Erie County41 of 791,65154.5%4.4 pCi/L
Butler County42 of 791,95354.3%4.4 pCi/L
Hocking County43 of 796053.3%4.0 pCi/L
Highland County ten-year laboratory totals, against Ohio's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestOhio, pooledChange from the row before
2008 to 20176756.7%4.8 pCi/L30.7 pCi/L52.3%+0.8 points
2007 to 20166855.9%4.5 pCi/L30.7 pCi/L52.8%+0.3 points
2006 to 20156355.6%4.5 pCi/L30.7 pCi/L52.9%−0.3 points
2005 to 20145955.9%4.5 pCi/L30.7 pCi/L52.4%First on file

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

Highland County, Geology

The ground under Highland County

Predicted

USGS's geologic map splits Highland County: 67.8% of its land is moderate radon potential and 32.2% high. The map puts 67.8% of Highland County in the area it calls Till Plains and 26.9% in Till Plains, 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 Highland County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Till PlainsOrdovician shale and limestone; glacial till.Moderate1167.8%
Till PlainsGlacial deposits underlain by Ordovician through Devonian limestone and shale.High1426.9%
Ohio ShaleDevonian-Mississippian black shale (includes some Ordovician limestone)High145.4%

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

Highland County beside the ground around it

Ohio as a whole has more high-potential ground than Highland County: 62.8% of its land, against 32.2% here. Of the 6 counties that border it, 5 have more high-potential ground, Fayette County the most at 100%.

Share of land by USGS radon potential: Highland County, the 6 counties bordering it and Ohio
AreaEPA zoneLow potentialModerate potentialHigh potential
Highland CountyZone 2None67.8%32.2%
Clinton CountyZone 1None26.0%74.0%
Fayette CountyZone 1NoneNone100%
Brown CountyZone 2None100%None
Adams CountyZone 1None41.7%58.3%
Pike CountyZone 1None1.5%98.5%
Ross CountyZone 1NoneNone100%
Ohio88 counties, pooled by land areaVariesNone37.2%62.8%

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

Local help

Highland County, Local resources

Radon testing and mitigation in Highland County

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

Highland County, Questions

Questions about radon in Highland County

Are radon levels high in Highland County?

Over the 2008 to 2017 laboratory totals, 56.7% of the radon tests reported to CDC for Highland County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.8 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 37 reported a higher share; pooled, the state comes to 52.3%.

Which counties border Highland County?

Highland County borders 6 counties: Clinton County, Fayette County, Brown County, Adams County, Pike County and Ross County.

Products

Highland County, Products

Testing a home in Highland County

In Highland County, 56.7% of 67 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 Highland County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Highland County homes, compared

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Highland County, Bordering counties

Counties bordering Highland County

Calculated by Radon411

Highland County, Cities and towns

Cities and towns in Highland County

The Census Bureau estimates 43,823 residents in Highland County for July 1, 2025, 460 more than in 2020 (+1.1%). That works out to 79 people per square mile of land. No town dominates: Hillsboro, the largest, has 6,763 residents, 15.4% of the total. Reported testing is thin here: 67 tests over 2008 to 2017, or 1.5 for every 1,000 residents (2025 estimate), where Ohio as a whole comes to 8.3.

From Hillsboro to Sinking Spring, CDC publishes no figure by town: each reads Highland County's.

The cities and towns in Highland County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Hillsboro6,763+5.0%15.4%
Greenfieldextends beyond Highland County4,329−0.3%Counted whole
Lynchburgextends beyond Highland County1,538+1.7%Counted whole
Leesburg1,280+0.8%2.9%
Sardiniaextends beyond Highland County1,101+1.8%Counted whole
Mowrystown387+0.3%0.9%
Highland229+0.4%0.5%
Sinking Spring120Level0.3%

8 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). A place that extends beyond Highland County is counted whole, so it has no share.

Highland County, Homes

Homes in Highland County

Of Highland County's 19,005 homes, 74% are detached houses, against 69% across Ohio; 14% are mobile homes. Much of Highland County is recent building: 17% of its homes have gone up since 2000 and the middle year built is 1979, against 1970 for Ohio. 73% 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 Highland County, Ohio, 2019 to 2023
HomesHighland CountyOhio
Housing units19,0055,271,573
Detached houses74%69%
In buildings of 5 or more4%15%
Mobile homes14%4%
Built before 196031%38%
Built since 200017%16%
Middle year built19791970
Owner-occupied73%67%

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