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Radon Levels in Johnson County, Tennessee

EPA puts Johnson County in Zone 2, its middle radon zone, and only 4 radon tests from it are on file with CDC (2023). 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

    34.4%

    1.1 pts above TN

    Johnson
    34.4%
    Tennessee
    33.3%

    157 tests, 2008 to 2017

  • Median result

    2.3pCi/L

    Below action level

    Johnson
    2.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    157

    31st of 80 by tests

    Johnson
    157
    Davidson
    5,592

    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 Tennessee

    32 of 80

    Middle half

    Johnson
    34.4%
    Jefferson
    56.8%

    By share, of 80 with 30+ tests

Read a result for Johnson County

Starts at Johnson County's median, 2.3 pCi/L

2.3pCi/L

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

EPA’s reading of 2.3 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. Johnson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Johnson County, At a glance

Johnson County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Johnson 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: High across 85% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Johnson County, 2023

Share of reported tests at or above 4 pCi/L, by year, Johnson County
Share of reported tests at or above 4 pCi/L, by year, Johnson County
YearShare of reported tests at or above 4 pCi/L
202236.4%
202350.0%

2023: 50.0%. Across these years the share ran from 36.4% to 50.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 4 tests were reported to CDC for Johnson County over 2023, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.

Measured: CDC tracking data. Figure above: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Johnson County, Compared

Johnson County radon figures, compared

Calculated by Radon411

In Johnson County, about 3 in 10 reported tests over the 2008 to 2017 laboratory totals (54 of 157) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 1.3 points lower. Across 95 Tennessee counties pooled together, 33.3% of tests reached that level, so Johnson County runs 1.1 points above its state.

The newest figure, in 2023, counts only 4 tests (50.0% at or above 4 pCi/L), too few to compare, so this reading uses the 157-test figure.

Of 7 neighbours with a figure, 6 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 34.1% (Ashe County, NC) to 58.1% (Washington County, VA). By share, Johnson County is 32nd of 80 Tennessee counties with 30 or more tests for the same period.

Half the tests came in under 2.3 pCi/L and half over it; the single highest reached 37.3 pCi/L. Below the action level, 65 tests (41.4%) came in under 2 pCi/L, against 42.4% statewide, and 38 tests (24.2%) fell between 2 and 4, against 24.3% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 34.4% share point the same way here. USGS geology rates 85% of the county's land high radon potential.

The busiest year on file was 2022, with 33 tests reported; the quietest, 2023, had 4.

Johnson County against Tennessee, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Johnson County
Johnson County15734.4%2.3 pCi/LThis county
Tennessee, pooled95 counties, pooled31,06633.3%Not pooled−1.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+1.3 points
Jefferson Countyhighest in the state14656.8%4.7 pCi/L+22.4 points
Chester Countylowest in the state440.0%1.1 pCi/L−34.4 points
Washington County, VAborders it38458.1%4.8 pCi/L+23.7 points
Sullivan County, TNborders it1,79951.5%4.2 pCi/L+17.1 points
Carter County, TNborders it34547.2%3.7 pCi/L+12.8 points
Watauga County, NCborders it1,21545.1%3.5 pCi/L+10.7 points
Grayson County, VAborders it4744.7%3.8 pCi/L+10.3 points
Avery County, NCborders it16038.8%2.8 pCi/L+4.4 points
Ashe County, NCborders it68134.1%2.5 pCi/L−0.3 points
Where Johnson County's reported results fell, 2008 to 2017, laboratory, beside Tennessee and the United States
ResultJohnson County testsJohnson County shareTennessee shareU.S. shareAgainst Tennessee
Under 2 pCi/L6541.4%42.4%39.6%−1.0 points
2 to 4 pCi/L3824.2%24.3%24.7%−0.1 points
4 pCi/L and above5434.4%33.3%35.7%+1.1 points
Johnson County ranked among the 80 Tennessee counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Davidson County27 of 805,59236.4%2.6 pCi/L
Putnam County28 of 8033636.0%2.6 pCi/L
Moore County29 of 805135.3%2.9 pCi/L
Hickman County30 of 8012035.0%2.2 pCi/L
Clay County31 of 804634.8%2.3 pCi/L
Johnson County32 of 8015734.4%2.3 pCi/L
Cheatham County33 of 8020534.1%2.3 pCi/L
McMinn County34 of 8010634.0%2.8 pCi/L
Montgomery County35 of 8059733.8%2.3 pCi/L
Roane County36 of 8025833.7%2.5 pCi/L
Knox County37 of 802,45233.6%2.5 pCi/L
Johnson County radon tests by year, against Tennessee's pooled share
YearTestsAt or above 4 pCi/LMedianHighestTennessee, pooledChange from the row before
2023450.0%4.7 pCi/L6.4 pCi/L24.9%+13.6 points
20223336.4%0.9 pCi/L14.7 pCi/L23.8%First on file

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

Johnson County, Geology

The ground under Johnson County

Predicted

Most of the ground under Johnson County is one class on USGS's geologic map: 85.1% of its land is high radon potential, with 14.9% moderate. The map puts 85.1% of Johnson County in the area it calls Ridge and Valley and 14.4% in Unaka Mountains. 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 Johnson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Ridge and ValleyPaleozoic sandstone and cherty dolostone.High1485.1%
Unaka MountainsPrecambrian and Paleozoic siltstone, sandstone, conglomerate, quartzite, phyllite, gneiss, granite, and metamorphosed volcanic rock.Moderate1114.4%

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

Johnson County beside the ground around it

Johnson County has more high-potential ground than Tennessee as a whole: 85.1% of its land against 47.2%. Of the 7 counties that border it, 2 have more high-potential ground, Sullivan County the most at 100%.

Share of land by USGS radon potential: Johnson County, the 7 counties bordering it and Tennessee
AreaEPA zoneLow potentialModerate potentialHigh potential
Johnson CountyZone 2None14.9%85.1%
Watauga County, NCZone 1None100%None
Carter CountyZone 2None39.5%60.5%
Ashe County, NCZone 2None100%None
Washington County, VAZone 1None1.4%98.6%
Avery County, NCZone 2None100%None
Sullivan CountyZone 1NoneNone100%
Grayson County, VAZone 2None97.5%2.5%
Tennessee95 counties, pooled by land areaVaries30.5%22.3%47.2%

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

Local help

Johnson County, Local resources

Radon testing and mitigation in Johnson County

What Tennessee's program says
Phone
1-800-232-1139
Email
TDEC.Radon@tn.gov

What it means

Johnson County, Questions

Questions about radon in Johnson County

Are radon levels high in Johnson County?

In 2023, 50.0% of the radon tests reported to CDC for Johnson County, Tennessee were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.7 pCi/L. Of 80 Tennessee counties with 30 or more tests for the same period, 31 reported a higher share; pooled, the state comes to 33.3%.

Which counties border Johnson County?

Johnson County borders 7 counties: Watauga County, NC, Carter County, TN, Ashe County, NC, Washington County, VA, Avery County, NC, Sullivan County, TN and Grayson County, VA.

Products

Johnson County, Products

Testing a home in Johnson County

In Johnson County, 34.4% of 157 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 33.3% pooled across Tennessee. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Johnson County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Johnson County homes, compared

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Johnson County, Bordering counties

Counties bordering Johnson County

Calculated by Radon411

Johnson County, Cities and towns

Cities and towns in Johnson County

The Census Bureau estimates 18,718 residents in Johnson County for July 1, 2025, 733 more than in 2020 (+4.1%). That works out to 63 people per square mile of land. Mountain City, its one incorporated place, has 2,490 residents, 13.3% of the total. Testing is reported here more often than across the state: CDC's 157 reported tests for 2008 to 2017 come to 8.4 for every 1,000 residents (2025 estimate), against 4.2 for Tennessee.

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

Mountain City, Johnson County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Mountain City2,490+3.8%13.3%

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).

Johnson County, Homes

Homes in Johnson County

Of Johnson County's 8,755 homes, 73% are detached houses, against 68% across Tennessee; 20% are mobile homes. Half of its homes were built before 1980, close to Tennessee's 1986: 23% date from before 1960 and 21% from 2000 or later. Owners live in 79% of the occupied homes (Tennessee: 67%), so for most households a test and a fix are their own to order.

Homes in Johnson County, Tennessee, 2019 to 2023
HomesJohnson CountyTennessee
Housing units8,7553,095,472
Detached houses73%68%
In buildings of 5 or more5%14%
Mobile homes20%8%
Built before 196023%18%
Built since 200021%29%
Middle year built19801986
Owner-occupied79%67%

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