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Radon Levels in Madison County, Ohio

EPA puts Madison County in Zone 1, its highest radon zone, and high results are common there: 67.4% of the 549 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

    67.4%

    15.1 pts above OH

    Madison
    67.4%
    Ohio
    52.3%

    549 tests, 2008 to 2017

  • Median result

    5.7pCi/L

    Action level reached

    Madison
    5.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    549

    36th of 79 by tests

    Madison
    549
    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

    10 of 79

    Top quarter

    Madison
    67.4%
    Pickaway
    81.4%

    By share, of 79 with 30+ tests

Read a result for Madison County

Starts at Madison County's median, 5.7 pCi/L

5.7pCi/L

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

EPA’s reading of 5.7 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. Madison County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Madison County, At a glance

Madison County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Madison County, 2008 to 2017, laboratory
Under 2 pCi/L: 11%2 to 4 pCi/L: 22%4 pCi/L and above: 67%

Of 549 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Madison County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L5910.7%
2 to 4 pCi/L12021.9%
4 pCi/L and above37067.4%
What these figures count

These are the 549 tests reported to CDC for Madison 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

Madison County, Compared

Madison County radon figures, compared

Calculated by Radon411

More than half: 67.4% of the 549 radon tests reported to CDC for Madison County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 10th of 79 Ohio counties with 30 or more tests for the same period. That is 15.1 points above the 52.3% pooled from 88 Ohio counties.

The median result, 5.7 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 104.0 pCi/L. The rest split 10.7% 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 67.4% share point the same way here.

3 of its 6 bordering counties with figures ran higher, led by Pickaway County at 81.4%; Clark County reported 57.5%. 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 Madison County went from 455 tests (2005 to 2014) to 549 (2008 to 2017), the share going from 63.5% to 67.4%.

Nationally, every county with a figure for the same period pools to 35.7%; Madison County sits 31.7 points above it. CDC also counts 27 tests taken after mitigation in Madison County for the same period: tests in homes where a fix was already in.

Madison County against Ohio, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Madison County
Madison County54967.4%5.7 pCi/LThis county
Ohio, pooled88 counties, pooled98,84052.3%Not pooled−15.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−31.7 points
Fairfield Countyhighest in the state1,17576.8%7.4 pCi/L+9.4 points
Cuyahoga Countylowest in the state10,09221.7%2.0 pCi/L−45.7 points
Pickaway County, OHborders it18381.4%9.5 pCi/L+14.0 points
Franklin County, OHborders it16,14271.9%6.8 pCi/L+4.5 points
Champaign County, OHborders it59671.1%6.8 pCi/L+3.7 points
Union County, OHborders it1,28560.2%4.8 pCi/L−7.2 points
Greene County, OHborders it2,60258.6%4.9 pCi/L−8.8 points
Fayette County, OHborders it1258.3%5.5 pCi/L−9.1 points
Clark County, OHborders it1,44757.5%4.9 pCi/L−9.9 points
Where Madison County's reported results fell, 2008 to 2017, laboratory, beside Ohio and the United States
ResultMadison County testsMadison County shareOhio shareU.S. shareAgainst Ohio
Under 2 pCi/L5910.7%23.1%39.6%−12.4 points
2 to 4 pCi/L12021.9%24.6%24.7%−2.7 points
4 pCi/L and above37067.4%52.3%35.7%+15.1 points
Madison 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
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
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
Madison County ten-year laboratory totals, against Ohio's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestOhio, pooledChange from the row before
2008 to 201754967.4%5.7 pCi/L104.0 pCi/L52.3%−0.3 points
2007 to 201649667.7%5.8 pCi/L104.0 pCi/L52.8%+1.4 points
2006 to 201546666.3%5.7 pCi/L104.0 pCi/L52.9%+2.8 points
2005 to 201445563.5%5.2 pCi/L104.0 pCi/L52.4%First on file

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

Madison County, Geology

The ground under Madison County

Predicted

USGS's geologic map puts all of Madison 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 Madison 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.

Madison County beside the ground around it

Madison 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; Champaign County comes nearest at 100%.

Share of land by USGS radon potential: Madison County, the 7 counties bordering it and Ohio
AreaEPA zoneLow potentialModerate potentialHigh potential
Madison CountyZone 1NoneNone100%
Clark CountyZone 1NoneNone100%
Franklin CountyZone 1NoneNone100%
Fayette CountyZone 1NoneNone100%
Pickaway CountyZone 1NoneNone100%
Champaign CountyZone 1NoneNone100%
Greene CountyZone 1NoneNone100%
Union CountyZone 1NoneNone100%
Ohio88 counties, pooled by land areaVariesNone37.2%62.8%

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

Local help

Madison County, Local resources

Radon testing and mitigation in Madison County

Listed radon businesses with an address in Madison County:

Listed radon professionals by town: London

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

Madison County, Questions

Questions about radon in Madison County

Are radon levels high in Madison County?

Over the 2008 to 2017 laboratory totals, 67.4% of the radon tests reported to CDC for Madison County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.7 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 9 reported a higher share; pooled, the state comes to 52.3%.

Which counties border Madison County?

Madison County borders 7 counties: Clark County, Franklin County, Fayette County, Pickaway County, Champaign County, Greene County and Union County.

Products

Madison County, Products

Testing a home in Madison County

In Madison County, 67.4% of 549 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 Madison 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

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

Explore

Madison County, Bordering counties

Counties bordering Madison County

Calculated by Radon411

Madison County, Cities and towns

Cities and towns in Madison County

Madison County is growing: the Census Bureau puts it at 46,985 residents on July 1, 2025, up 7.1% from 43,864 in 2020. That works out to 101 people per square mile of land. Its largest town, London, has 10,813 residents, 23.0% of the total. CDC's 549 reported tests for 2008 to 2017 work out to 11.7 per 1,000 residents (2025 estimate), close to Ohio's 8.3.

From London to Midway, CDC publishes no figure by town: each reads Madison County's.

The cities and towns in Madison County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
London10,813+5.4%23.0%
West Jefferson5,827+40.3%12.4%
Plain Cityextends beyond Madison County4,322+4.0%Counted whole
Mount Sterling2,051+5.7%4.4%
South Solon327+0.3%0.7%
Midway270Level0.6%

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

Madison County, Homes

Homes in Madison County

Madison County is a place of houses on their own lots: 79% of its 16,361 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1975, close to Ohio's 1970: 33% date from before 1960 and 17% from 2000 or later. Owners live in 76% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.

Homes in Madison County, Ohio, 2019 to 2023
HomesMadison CountyOhio
Housing units16,3615,271,573
Detached houses79%69%
In buildings of 5 or more8%15%
Mobile homes5%4%
Built before 196033%38%
Built since 200017%16%
Middle year built19751970
Owner-occupied76%67%

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