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Radon Levels in Knox County, Ohio

EPA puts Knox County in Zone 1, its highest radon zone, and high results are common there: 72.0% of the 1,530 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

    72.0%

    19.7 pts above OH

    Knox
    72.0%
    Ohio
    52.3%

    1,530 tests, 2008 to 2017

  • Median result

    8.1pCi/L

    Action level reached

    Knox
    8.1 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,530

    17th of 79 by tests

    Knox
    1,530
    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

    5 of 79

    Top quarter

    Knox
    72.0%
    Pickaway
    81.4%

    By share, of 79 with 30+ tests

Read a result for Knox County

Starts at Knox County's median, 8.1 pCi/L

8.1pCi/L

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

EPA’s reading of 8.1 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. Knox County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Knox County, At a glance

Knox County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Knox 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 Knox County, 2008 to 2017, laboratory

Reported results by concentration band, Knox County, 2008 to 2017, laboratory
Under 2 pCi/L: 13%2 to 4 pCi/L: 15%4 pCi/L and above: 72%

Of 1,530 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Knox County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L19112.5%
2 to 4 pCi/L23715.5%
4 pCi/L and above1,10272.0%
What these figures count

These are the 1,530 tests reported to CDC for Knox 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

Knox County, Compared

Knox County radon figures, compared

Calculated by Radon411

More than half: 72.0% of the 1,530 radon tests reported to CDC for Knox County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 5th of 79 Ohio counties with 30 or more tests for the same period. That is 19.7 points above the 52.3% pooled from 88 Ohio counties.

The median result, 8.1 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 610.3 pCi/L. The rest split 12.5% under 2 pCi/L and 15.5% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 72.0% share point the same way here.

1 of its 7 bordering counties with figures ran higher, led by Delaware County at 72.2%; Coshocton County reported 58.9%. 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 Knox County went from 1,647 tests (2005 to 2014) to 1,530 (2008 to 2017), the share going from 71.2% to 72.0%.

Nationally, every county with a figure for the same period pools to 35.7%; Knox County sits 36.3 points above it. CDC also counts 73 tests taken after mitigation in Knox County for the same period: tests in homes where a fix was already in.

Knox County against Ohio, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Knox County
Knox County1,53072.0%8.1 pCi/LThis county
Ohio, pooled88 counties, pooled98,84052.3%Not pooled−19.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−36.3 points
Pickaway Countyhighest in the state18381.4%9.5 pCi/L+9.4 points
Cuyahoga Countylowest in the state10,09221.7%2.0 pCi/L−50.3 points
Delaware County, OHborders it3,73072.2%6.4 pCi/L+0.2 points
Licking County, OHborders it4,69471.2%7.0 pCi/L−0.8 points
Morrow County, OHborders it17765.0%5.7 pCi/L−7.0 points
Holmes County, OHborders it6764.2%5.8 pCi/L−7.8 points
Ashland County, OHborders it34062.9%5.4 pCi/L−9.1 points
Richland County, OHborders it1,32762.2%5.2 pCi/L−9.8 points
Coshocton County, OHborders it11258.9%5.1 pCi/L−13.1 points
Where Knox County's reported results fell, 2008 to 2017, laboratory, beside Ohio and the United States
ResultKnox County testsKnox County shareOhio shareU.S. shareAgainst Ohio
Under 2 pCi/L19112.5%23.1%39.6%−10.6 points
2 to 4 pCi/L23715.5%24.6%24.7%−9.1 points
4 pCi/L and above1,10272.0%52.3%35.7%+19.7 points
Knox 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
Pickaway County1 of 7918381.4%9.5 pCi/L
Fairfield County2 of 791,17576.8%7.4 pCi/L
Logan County3 of 7975573.6%7.9 pCi/L
Delaware County4 of 793,73072.2%6.4 pCi/L
Knox County5 of 791,53072.0%8.1 pCi/L
Franklin County6 of 7916,14271.9%6.8 pCi/L
Licking County7 of 794,69471.2%7.0 pCi/L
Auglaize County8 of 7913971.2%6.5 pCi/L
Champaign County9 of 7959671.1%6.8 pCi/L
Madison County10 of 7954967.4%5.7 pCi/L
Ross County11 of 7936867.1%7.0 pCi/L
Knox County ten-year laboratory totals, against Ohio's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestOhio, pooledChange from the row before
2008 to 20171,53072.0%8.1 pCi/L610.3 pCi/L52.3%+0.4 points
2007 to 20161,54971.6%8.2 pCi/L610.3 pCi/L52.8%+0.1 points
2006 to 20151,62671.5%8.2 pCi/L641.8 pCi/L52.9%+0.3 points
2005 to 20141,64771.2%7.8 pCi/L641.8 pCi/L52.4%First on file

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

Knox County, Geology

The ground under Knox County

Predicted

USGS's geologic map puts all of Knox County's mapped land in one class: high radon potential. The map puts 55.4% of Knox County in the area it calls Till Plains and 42.0% in Glaciated Plateau, with one smaller area beside them. USGS gives the first a radon index of 14 and the second 12, both in the high band (12 to 17).

USGS's geologic areas under Knox County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Till PlainsGlacial deposits underlain by Ordovician through Devonian limestone and shale.High1455.4%
Glaciated PlateauPre-Wisconsin glacial deposits derived from high radioactivity marine black shale.High1242.0%
Area of Elevated RadioactivityPennsylvanian shale, sandstone, coal, and limestone.High122.6%

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

Knox County beside the ground around it

Knox County has more high-potential ground than Ohio as a whole: 100% of its land against 62.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Delaware County comes nearest at 100%.

Share of land by USGS radon potential: Knox County, the 7 counties bordering it and Ohio
AreaEPA zoneLow potentialModerate potentialHigh potential
Knox CountyZone 1NoneNone100%
Morrow CountyZone 1NoneNone100%
Licking CountyZone 1NoneNone100%
Richland CountyZone 1None6.3%93.7%
Holmes CountyZone 1NoneNone100%
Coshocton CountyZone 1NoneNone100%
Ashland CountyZone 1None31.5%68.5%
Delaware CountyZone 1NoneNone100%
Ohio88 counties, pooled by land areaVariesNone37.2%62.8%

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

Local help

Knox County, Local resources

Radon testing and mitigation in Knox County

Listed radon businesses with an address in Knox County:

Listed radon professionals by town: Danville

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

Knox County, Questions

Questions about radon in Knox County

Are radon levels high in Knox County?

Over the 2008 to 2017 laboratory totals, 72.0% of the radon tests reported to CDC for Knox County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 8.1 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 4 reported a higher share; pooled, the state comes to 52.3%.

Which counties border Knox County?

Knox County borders 7 counties: Morrow County, Licking County, Richland County, Holmes County, Coshocton County, Ashland County and Delaware County.

Products

Knox County, Products

Testing a home in Knox County

In Knox County, 72.0% of 1,530 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 Knox 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

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

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Knox County, Bordering counties

Counties bordering Knox County

Calculated by Radon411

Knox County, Cities and towns

Cities and towns in Knox County

The Census Bureau estimates 64,002 residents in Knox County for July 1, 2025, 1,198 more than in 2020 (+1.9%). That works out to 122 people per square mile of land. Its largest town, Mount Vernon, has 17,287 residents, 27.0% of the total. Testing is reported here more often than across the state: CDC's 1,530 reported tests for 2008 to 2017 come to 23.9 for every 1,000 residents (2025 estimate), against 8.3 for Ohio.

From Mount Vernon to Gann (Brinkhaven), CDC publishes no figure by town: each reads Knox County's.

The 7 largest cities and towns in Knox County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Mount Vernon17,287+1.3%27.0%
Fredericktown2,658+0.3%4.2%
Gambier2,233+0.5%3.5%
Uticaextends beyond Knox County2,138+3.2%Counted whole
Centerburg1,691−2.1%2.6%
Danville1,025+0.1%1.6%
Martinsburg222−1.8%0.3%
  • Gann (Brinkhaven)

8 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 Knox County is counted whole, so it has no share.

Knox County, Homes

Homes in Knox County

Knox County is a place of houses on their own lots: 83% of its 26,038 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1972, close to Ohio's 1970: 40% date from before 1960 and 18% from 2000 or later. Owners live in 75% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.

Homes in Knox County, Ohio, 2019 to 2023
HomesKnox CountyOhio
Housing units26,0385,271,573
Detached houses83%69%
In buildings of 5 or more4%15%
Mobile homes3%4%
Built before 196040%38%
Built since 200018%16%
Middle year built19721970
Owner-occupied75%67%

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