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Radon Levels in Jefferson County, Kentucky

EPA puts Jefferson County in Zone 1, its highest radon zone, and 39.4% of its 6,590 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    39.4%

    4.3 pts below KY

    Jefferson
    39.4%
    Kentucky
    43.7%

    6,590 tests, 2008 to 2017

  • Median result

    2.7pCi/L

    Below action level

    Jefferson
    2.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    6,590

    Most tested in Kentucky

    Jefferson
    6,590

    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 Kentucky

    29 of 69

    Middle half

    Jefferson
    39.4%
    Meade
    68.4%

    By share, of 69 with 30+ tests

Read a result for Jefferson County

Starts at Jefferson County's median, 2.7 pCi/L

2.7pCi/L

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

EPA’s reading of 2.7 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. Jefferson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Jefferson County, At a glance

Jefferson County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Jefferson 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 55% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Jefferson County, 2008 to 2017, laboratory
Under 2 pCi/L: 40%2 to 4 pCi/L: 21%4 pCi/L and above: 39%

Of 6,590 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Jefferson County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2,64240.1%
2 to 4 pCi/L1,35420.5%
4 pCi/L and above2,59439.4%
What these figures count

These are the 6,590 tests reported to CDC for Jefferson 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

Jefferson County, Compared

Jefferson County radon figures, compared

Calculated by Radon411

In Jefferson County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (2,594 of 6,590) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 3.7 points higher. Across 120 Kentucky counties pooled together, 43.7% of tests reached that level, so Jefferson County runs 4.3 points below its state.

Of 8 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 31.3% (Spencer County) to 62.4% (Harrison County, IN). By share, Jefferson County is 29th of 69 Kentucky counties with 30 or more tests for the same period.

Half the tests came in under 2.7 pCi/L and half over it; the single highest reached 155.3 pCi/L. Below the action level, 2,642 tests (40.1%) came in under 2 pCi/L, against 33.2% statewide, and 1,354 tests (20.5%) fell between 2 and 4, against 23.1% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 39.4% share point the same way here. USGS geology rates 55% of the county's land high radon potential. CDC also counts 275 tests taken after mitigation in Jefferson County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Jefferson County went from 3,989 tests (2005 to 2014) to 6,590 (2008 to 2017), the share going from 48.0% to 39.4%.

Jefferson County against Kentucky, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Jefferson County
Jefferson County6,59039.4%2.7 pCi/LThis county
Kentucky, pooled120 counties, pooled28,79343.7%Not pooled+4.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−3.7 points
Meade Countyhighest in the state11768.4%8.2 pCi/L+29.0 points
Hopkins Countylowest in the state429.5%1.7 pCi/L−29.9 points
Harrison County, INborders it22162.4%5.5 pCi/L+23.0 points
Hardin County, KYborders it42950.3%4.0 pCi/L+10.9 points
Clark County, INborders it51247.7%3.6 pCi/L+8.3 points
Bullitt County, KYborders it55147.5%3.6 pCi/L+8.1 points
Floyd County, INborders it31642.4%3.3 pCi/L+3.0 points
Shelby County, KYborders it40737.6%3.0 pCi/L−1.8 points
Oldham County, KYborders it80337.1%2.7 pCi/L−2.3 points
Spencer County, KYborders it16631.3%2.5 pCi/L−8.1 points
Where Jefferson County's reported results fell, 2008 to 2017, laboratory, beside Kentucky and the United States
ResultJefferson County testsJefferson County shareKentucky shareU.S. shareAgainst Kentucky
Under 2 pCi/L2,64240.1%33.2%39.6%+6.9 points
2 to 4 pCi/L1,35420.5%23.1%24.7%−2.6 points
4 pCi/L and above2,59439.4%43.7%35.7%−4.3 points
Jefferson 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
Estill County24 of 6917744.1%3.2 pCi/L
Adair County25 of 695343.4%3.8 pCi/L
Franklin County26 of 6981043.1%3.3 pCi/L
Boone County27 of 691,43442.9%3.5 pCi/L
Garrard County28 of 6916439.6%2.6 pCi/L
Jefferson County29 of 696,59039.4%2.7 pCi/L
Madison County30 of 6960438.7%2.9 pCi/L
Mercer County31 of 6928838.2%2.7 pCi/L
Shelby County32 of 6940737.6%3.0 pCi/L
Oldham County33 of 6980337.1%2.7 pCi/L
Henry County34 of 694136.6%3.2 pCi/L
Jefferson County ten-year laboratory totals, against Kentucky's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestKentucky, pooledChange from the row before
2008 to 20176,59039.4%2.7 pCi/L155.3 pCi/L43.7%−3.2 points
2007 to 20165,58142.6%3.1 pCi/L155.3 pCi/L45.1%−2.5 points
2006 to 20154,60645.1%3.4 pCi/L155.3 pCi/L46.4%−2.9 points
2005 to 20143,98948.0%3.7 pCi/L155.3 pCi/L47.3%First on file

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

Jefferson County, Geology

The ground under Jefferson County

Predicted

USGS's geologic map splits Jefferson County: 55.1% of its land is high radon potential and 44.9% moderate. The map puts 54.9% of Jefferson County in the area it calls New Albany-Chattanooga Shale and 25.1% in Outer Bluegrass, with 2 smaller areas beside them. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Jefferson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
New Albany-Chattanooga ShaleDevonian/Mississippian Black shale.High1454.9%
Outer BluegrassOrdovician-Devonian limestone and shale.Moderate1125.1%
Mississippian PlateauMississippian marine limestones, dolomites, marine sandstones, siltstones, and shales.Moderate1119.3%
Crawford Upland/Mitchell Plain/Norman UplandUnglaciated, underlain by karsted Mississippian carbonate rocks.Moderate110.6%

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

Jefferson County beside the ground around it

Jefferson County has more high-potential ground than Kentucky as a whole: 55.1% of its land against 18.2%. Of the 8 counties that border it, 1 has more high-potential ground, Bullitt County the most at 73.4%.

Share of land by USGS radon potential: Jefferson County, the 8 counties bordering it and Kentucky
AreaEPA zoneLow potentialModerate potentialHigh potential
Jefferson CountyZone 1None44.9%55.1%
Floyd County, INZone 2None95.7%4.3%
Bullitt CountyZone 1None26.6%73.4%
Oldham CountyZone 2None48.3%51.7%
Clark County, INZone 1None49.1%50.9%
Spencer CountyZone 2None100%None
Shelby CountyZone 2None100%None
Harrison County, INZone 1None100%None
Hardin CountyZone 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

Jefferson County, Local resources

Radon testing and mitigation in Jefferson County

Listed radon businesses with an address in Jefferson County:

Listed radon professionals by town: Louisville

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

What it means

Jefferson County, Questions

Questions about radon in Jefferson County

Are radon levels high in Jefferson County?

Over the 2008 to 2017 laboratory totals, 39.4% of the radon tests reported to CDC for Jefferson County, Kentucky were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.7 pCi/L. Of 69 Kentucky counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 43.7%.

Which counties border Jefferson County?

Jefferson County borders 8 counties: Floyd County, IN, Bullitt County, KY, Oldham County, KY, Clark County, IN, Spencer County, KY, Shelby County, KY, Harrison County, IN and Hardin County, KY.

Products

Jefferson County, Products

Testing a home in Jefferson County

In Jefferson County, 39.4% of 6,590 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 43.7% pooled across Kentucky. In Zone 1 the year-round level in Jefferson 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

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

Explore

Jefferson County, Bordering counties

Counties bordering Jefferson County

Calculated by Radon411

Jefferson County, Cities and towns

Cities and towns in Jefferson County

The Census Bureau estimates 795,222 residents in Jefferson County for July 1, 2025, 12,356 more than in 2020 (+1.6%). Packed into its land, that is 2,088 people per square mile. No town dominates: Jeffersontown, the largest, has 29,193 residents, 3.7% of the total. CDC's 6,590 reported tests for 2008 to 2017 work out to 8.3 per 1,000 residents (2025 estimate), close to Kentucky's 6.3.

From Jeffersontown to Louisville, CDC publishes no figure by town: each reads Jefferson County's.

The 12 largest cities and towns in Jefferson County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Jeffersontown29,193−0.1%3.7%
St. Matthews17,868+1.8%2.2%
Shively15,895+1.6%2.0%
Lyndon11,301+2.2%1.4%
Middletown9,944+2.4%1.3%
Douglass Hills5,575+2.1%0.7%
Hurstbourne4,787+2.1%0.6%
Prospectextends beyond Jefferson County4,705+2.4%Counted whole
Indian Hills2,939+1.8%0.4%
Graymoor-Devondale2,832−0.5%0.4%
Anchorage2,547+1.9%0.3%
Windy Hills2,476+1.9%0.3%
  • Hurstbourne Acres
  • Worthington Hills
  • St. Regis Park
  • Audubon Park
  • West Buechel
  • Coldstream
  • Beechwood Village
  • Heritage Creek
  • Barbourmeade
  • Watterson Park
  • Northfield
  • Lynnview
  • Woodlawn Park
  • Rolling Hills
  • Bellemeade
  • Langdon Place
  • Fincastle
  • Plantation
  • Hollow Creek
  • Blue Ridge Manor
  • Woodland Hills
  • Meadow Vale
  • Green Spring
  • Rolling Fields
The other 47 places in Jefferson County
  • Strathmoor Village
  • Spring Valley
  • Seneca Gardens
  • Brownsboro Farm
  • Parkway Village
  • Glenview
  • Westwood
  • Murray Hill
  • Wellington
  • Hollyvilla
  • Bancroft
  • Houston Acres
  • Riverwood
  • Briarwood
  • Forest Hills
  • Norbourne Estates
  • Moorland
  • Meadowview Estates
  • Richlawn
  • Kingsley
  • Poplar Hills
  • Norwood
  • Glenview Hills
  • Old Brownsboro Place
  • Strathmoor Manor
  • Bellewood
  • Brownsboro Village
  • Creekside
  • Goose Creek
  • Druid Hills
  • Spring Mill
  • Wildwood
  • Broeck Pointe
  • Manor Creek
  • Crossgate
  • Glenview Manor
  • Mockingbird Valley
  • Thornhill
  • Maryhill Estates
  • Sycamore
  • Cambridge
  • Hills and Dales
  • Lincolnshire
  • Hickory Hill
  • Meadowbrook Farm
  • Ten Broeck
  • South Park View

84 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 Jefferson County is counted whole, so it has no share.

Jefferson County, Homes

Homes in Jefferson County

Of Jefferson County's 357,923 homes, 64% are detached houses, against 68% across Kentucky; 21% are in buildings of five or more homes. The homes are older than Kentucky's as a whole: half were built before 1971 (1982 for Kentucky), and 35% date from before 1960. 62% 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 Jefferson County, Kentucky, 2019 to 2023
HomesJefferson CountyKentucky
Housing units357,9232,010,655
Detached houses64%68%
In buildings of 5 or more21%12%
Mobile homes1%11%
Built before 196035%22%
Built since 200019%24%
Middle year built19711982
Owner-occupied62%68%

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