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Radon Levels in Simpson County, Kentucky

EPA puts Simpson County in Zone 2, its middle radon zone, and 32.5% of its 126 reported radon tests (2008 to 2017, laboratory totals) were 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

    32.5%

    11.2 pts below KY

    Simpson
    32.5%
    Kentucky
    43.7%

    126 tests, 2008 to 2017

  • Median result

    2.6pCi/L

    Below action level

    Simpson
    2.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    126

    31st of 69 by tests

    Simpson
    126
    Jefferson
    6,590

    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 Kentucky

    40 of 69

    Middle half

    Simpson
    32.5%
    Meade
    68.4%

    By share, of 69 with 30+ tests

Read a result for Simpson County

Starts at Simpson County's median, 2.6 pCi/L

2.6pCi/L

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

EPA’s reading of 2.6 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. Simpson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Simpson County, At a glance

Simpson County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Simpson 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Simpson County, 2008 to 2017, laboratory
Under 2 pCi/L: 40%2 to 4 pCi/L: 28%4 pCi/L and above: 32%

Of 126 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Simpson County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L5039.7%
2 to 4 pCi/L3527.8%
4 pCi/L and above4132.5%
What these figures count

These are the 126 tests reported to CDC for Simpson 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

Simpson County, Compared

Simpson County radon figures, compared

Calculated by Radon411

In Simpson County, about 3 in 10 reported tests over the 2008 to 2017 laboratory totals (41 of 126) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 3.2 points lower. Across 120 Kentucky counties pooled together, 43.7% of tests reached that level, so Simpson County runs 11.2 points below its state.

Of 5 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 26.0% (Sumner County, TN) to 61.5% (Warren County). By share, Simpson County is 40th of 69 Kentucky counties with 30 or more tests for the same period.

Half the tests came in under 2.6 pCi/L and half over it; the single highest reached 46.3 pCi/L. Below the action level, 50 tests (39.7%) came in under 2 pCi/L, against 33.2% statewide, and 35 tests (27.8%) fell between 2 and 4, against 23.1% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 32.5% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential.

CDC's ten-year totals for Simpson County went from 124 tests (2005 to 2014) to 126 (2008 to 2017), the share going from 32.3% to 32.5%.

Simpson County against Kentucky, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Simpson County
Simpson County12632.5%2.6 pCi/LThis county
Kentucky, pooled120 counties, pooled28,79343.7%Not pooled+11.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+3.2 points
Meade Countyhighest in the state11768.4%8.2 pCi/L+35.9 points
Hopkins Countylowest in the state429.5%1.7 pCi/L−23.0 points
Warren County, KYborders it1,62461.5%6.3 pCi/L+29.0 points
Logan County, KYborders it7931.6%2.4 pCi/L−0.9 points
Allen County, KYborders it5829.3%1.9 pCi/L−3.2 points
Robertson County, TNborders it27328.9%1.9 pCi/L−3.6 points
Sumner County, TNborders it1,31126.0%1.9 pCi/L−6.5 points
Where Simpson County's reported results fell, 2008 to 2017, laboratory, beside Kentucky and the United States
ResultSimpson County testsSimpson County shareKentucky shareU.S. shareAgainst Kentucky
Under 2 pCi/L5039.7%33.2%39.6%+6.5 points
2 to 4 pCi/L3527.8%23.1%24.7%+4.7 points
4 pCi/L and above4132.5%43.7%35.7%−11.2 points
Simpson County ranked among the 69 Kentucky counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Owen County35 of 695836.2%2.5 pCi/L
Christian County36 of 697236.1%3.2 pCi/L
Lincoln County37 of 6913535.6%2.8 pCi/L
Grant County38 of 697833.3%2.5 pCi/L
Casey County39 of 694332.6%3.1 pCi/L
Simpson County40 of 6912632.5%2.6 pCi/L
Green County41 of 693132.3%2.5 pCi/L
Carter County42 of 694131.7%2.2 pCi/L
Logan County43 of 697931.6%2.4 pCi/L
Spencer County44 of 6916631.3%2.5 pCi/L
Breckinridge County45 of 693231.3%2.5 pCi/L
Simpson County ten-year laboratory totals, against Kentucky's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestKentucky, pooledChange from the row before
2008 to 201712632.5%2.6 pCi/L46.3 pCi/L43.7%−1.1 points
2007 to 201612833.6%2.6 pCi/L46.7 pCi/L45.1%−0.2 points
2006 to 201513033.8%2.7 pCi/L46.7 pCi/L46.4%+1.5 points
2005 to 201412432.3%2.6 pCi/L46.7 pCi/L47.3%First on file

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

Simpson County, Geology

The ground under Simpson County

Predicted

USGS's geologic map puts all of Simpson County's mapped land in one class: moderate radon potential. 99.0% of it lies in the area the map calls Mississippian Plateau, to which USGS gives a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under Simpson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Mississippian PlateauMississippian marine limestones, dolomites, marine sandstones, siltstones, and shales.Moderate1199.0%
Highland RimPaleozoic sedimentary rocks (limestone, shale, chert, and dolostone).Moderate111.0%

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

Simpson County beside the ground around it

Across Kentucky 18.2% of the land is rated high; none of Simpson County's is. Of the 5 counties that border it, 4 have more high-potential ground, Sumner County, TN the most at 79.6%.

Share of land by USGS radon potential: Simpson County, the 5 counties bordering it and Kentucky
AreaEPA zoneLow potentialModerate potentialHigh potential
Simpson CountyZone 2None100%None
Warren CountyZone 1None99.9%0.1%
Logan CountyZone 2None100%None
Allen CountyZone 1None38.5%61.5%
Sumner County, TNZone 2None20.4%79.6%
Robertson County, TNZone 2None96.6%3.4%
Kentucky120 counties, pooled by land areaVaries5.7%76.1%18.2%

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

Local help

Simpson County, Local resources

Radon testing and mitigation in Simpson County

What Kentucky's program says
Phone
502-782-2782
Email
Radon@ky.gov

What it means

Simpson County, Questions

Questions about radon in Simpson County

Are radon levels high in Simpson County?

Over the 2008 to 2017 laboratory totals, 32.5% of the radon tests reported to CDC for Simpson County, Kentucky were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.6 pCi/L. Of 69 Kentucky counties with 30 or more tests for the same period, 39 reported a higher share; pooled, the state comes to 43.7%.

Which counties border Simpson County?

Simpson County borders 5 counties: Warren County, KY, Logan County, KY, Allen County, KY, Sumner County, TN and Robertson County, TN.

Products

Simpson County, Products

Testing a home in Simpson County

In Simpson County, 32.5% of 126 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 43.7% pooled across Kentucky. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Simpson County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Simpson County homes, compared

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Simpson County, Bordering counties

Counties bordering Simpson County

Calculated by Radon411

Simpson County, Cities and towns

Cities and towns in Simpson County

Simpson County is growing: the Census Bureau puts it at 20,788 residents on July 1, 2025, up 5.9% from 19,628 in 2020. That works out to 89 people per square mile of land. Franklin, its one incorporated place, has 10,759 residents, 51.8% of the total. CDC's 126 reported tests for 2008 to 2017 work out to 6.1 per 1,000 residents (2025 estimate), close to Kentucky's 6.3.

Franklin is the one incorporated place here; CDC publishes no figure by town, so it reads Simpson County's.

Franklin, Simpson County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Franklin10,759+5.3%51.8%

One incorporated place, 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).

Simpson County, Homes

Homes in Simpson County

Simpson County is a place of houses on their own lots: 79% of its 8,456 homes are detached single-family houses, against 68% across Kentucky. Half of its homes were built before 1979, close to Kentucky's 1982: 25% date from before 1960 and 23% from 2000 or later. 66% of occupied homes are lived in by their owner (Kentucky: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Simpson County, Kentucky, 2019 to 2023
HomesSimpson CountyKentucky
Housing units8,4562,010,655
Detached houses79%68%
In buildings of 5 or more7%12%
Mobile homes8%11%
Built before 196025%22%
Built since 200023%24%
Middle year built19791982
Owner-occupied66%68%

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