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Radon Levels in Johnston County, North Carolina

EPA puts Johnston County in Zone 3, its lowest radon zone, and only 3 radon tests from it are on file with CDC (2022). 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

    8.2%

    14.4 pts below NC

    Johnston
    8.2%
    NC
    22.6%

    668 tests, 2008 to 2017

  • Median result

    0.7pCi/L

    Below action level

    Johnston
    0.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    668

    28th of 75 by tests

    Johnston
    668
    Wake
    9,694

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 3

    Lower potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    EPA predicts under 2 pCi/L indoors

  • Rank in NC

    56 of 75

    Middle half

    Johnston
    8.2%
    Transylvania
    47.8%

    By share, of 75 with 30+ tests

Read a result for Johnston County

Starts at Johnston County's median, 0.7 pCi/L

0.7pCi/L

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

EPA’s reading of 0.7 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Johnston County's median reported result, 2008 to 2017.

Interpret this reading

The data

Johnston County, At a glance

Johnston County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Johnston County as a whole is an average indoor of less than 2 pCi/L (less than 75 Bq/m³). A low zone clears no address in it: homes above EPA's turn up in all three zones.

USGS geologic potential: Low across 69% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Johnston County, 2022

Share of reported tests at or above 4 pCi/L, by year, Johnston County
Share of reported tests at or above 4 pCi/L, by year, Johnston County
YearShare of reported tests at or above 4 pCi/L
201415.6%
20205.3%
20213.6%
20220.0%

2022: 0.0%. Across these years the share ran from 0.0% to 15.6%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 3 tests were reported to CDC for Johnston County over 2022, 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: 2022. Measured data period: 2005 to 2022 (every CDC figure on file).

How to read these figures

Johnston County, Compared

Johnston County radon figures, compared

Calculated by Radon411

Johnston County reports fewer high tests than North Carolina overall. 8.2% of its 668 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 14.4 points below the 22.6% pooled from 99 North Carolina counties.

The newest figure, in 2022, counts only 3 tests (0.0% at or above 4 pCi/L), too few to compare, so this reading uses the 668-test figure.

Ordered from highest share down, it comes 56th of 75 North Carolina counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; Johnston County sits 27.5 points below it.

Next door, the shares run from 0.0% in Nash County to 19.1% in Franklin County, with Harnett County and Nash County below Johnston County. Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 8.2% share point the same way here.

Half the tests came in under 0.7 pCi/L and half over it; the single highest reached 23.2 pCi/L. The rest split 80.8% under 2 pCi/L and 10.9% from 2 to 4 (North Carolina: 55.6% and 21.8%). Year by year, 2014 opened at 15.6% and 2021 closed at 3.6% (down 12.0 points), with 2014 the high at 15.6%.

The busiest year on file was 2020, with 114 tests reported; the quietest, 2022, had 3.

Share of reported tests at or above 4 pCi/L by year, Johnston County against North Carolina2014 to 2021, years with 30 or more tests: Johnston County 15.6% to 3.6%, the state's pooled share 14.9% in 2021.
Johnston CountyNorth Carolina, pooled
Share of reported tests at or above 4 pCi/L by year, Johnston County against North Carolina: data table
YearTestsJohnston County, at or above 4 pCi/LNorth Carolina, pooled
20144515.6%21.9%
20201145.3%21.1%
2021563.6%14.9%
Johnston County against North Carolina, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Johnston County
Johnston County6688.2%0.7 pCi/LThis county
North Carolina, pooled99 counties, pooled73,13922.6%Not pooled+14.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+27.5 points
Transylvania Countyhighest in the state3,86247.8%3.7 pCi/L+39.6 points
Columbus Countylowest in the state310.0%0.1 pCi/L−8.2 points
Franklin County, NCborders it20419.1%1.4 pCi/L+10.9 points
Wake County, NCborders it9,6949.6%1.0 pCi/L+1.4 points
Wayne County, NCborders it498.2%0.6 pCi/LLevel
Harnett County, NCborders it1810.6%0.6 pCi/L−7.6 points
Sampson County, NCborders it130.0%0.6 pCi/L−8.2 points
Nash County, NCborders it300.0%0.2 pCi/L−8.2 points
Wilson County, NCborders it170.0%0.4 pCi/L−8.2 points
Where Johnston County's reported results fell, 2008 to 2017, laboratory, beside North Carolina and the United States
ResultJohnston County testsJohnston County shareNorth Carolina shareU.S. shareAgainst North Carolina
Under 2 pCi/L54080.8%55.6%39.6%+25.2 points
2 to 4 pCi/L7310.9%21.8%24.7%−10.9 points
4 pCi/L and above558.2%22.6%35.7%−14.4 points
Johnston County ranked among the 75 North Carolina counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Orange County51 of 751,09510.7%1.1 pCi/L
Granville County52 of 7515310.5%0.8 pCi/L
Wake County53 of 759,6949.6%1.0 pCi/L
Cabarrus County54 of 758808.8%1.0 pCi/L
Mecklenburg County55 of 753,7538.5%0.9 pCi/L
Johnston County56 of 756688.2%0.7 pCi/L
Wayne County57 of 75498.2%0.6 pCi/L
Guilford County58 of 756,8707.9%0.9 pCi/L
Randolph County59 of 754227.1%0.9 pCi/L
Durham County60 of 751,5704.3%0.7 pCi/L
Robeson County61 of 75533.8%0.8 pCi/L
Johnston County radon tests by year, against North Carolina's pooled share
YearTestsAt or above 4 pCi/LMedianHighestNorth Carolina, pooledChange from the row before
202230.0%0.1 pCi/L1.0 pCi/L10.7%−3.6 points
2021563.6%0.1 pCi/L8.0 pCi/L14.9%−1.7 points
20201145.3%0.4 pCi/L8.5 pCi/L21.1%−10.3 points
20144515.6%0.8 pCi/L10.0 pCi/L21.9%First on file

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

Johnston County, Geology

The ground under Johnston County

Predicted

USGS's geologic map splits Johnston County: 69.1% of its land is low radon potential and 30.9% moderate. The map puts 45.6% of Johnston County in the area it calls Inner Coastal Plain and 30.9% in Raleigh Belt, with one smaller area beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Johnston County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Inner Coastal PlainFossiliferous clay and sand, shelly sand, sandy marl, and limestone.Low845.6%
Raleigh BeltProterozoic through Cambrian biotite gneiss and mica schist.Moderate1130.9%
Eastern Slate BeltProterozoic to Cambrian metamudstone and argillite, interbedded with metamorphosed sandstone, conglomerate, and volcanic rock.Low823.5%

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

Johnston County beside the ground around it

Across North Carolina 1.3% of the land is rated high; none of Johnston County's is. Of the 7 counties that border it, 2 have more moderate-potential ground, Franklin County the most at 99.8%.

Share of land by USGS radon potential: Johnston County, the 7 counties bordering it and North Carolina
AreaEPA zoneLow potentialModerate potentialHigh potential
Johnston CountyZone 369.1%30.9%None
Wake CountyZone 220.6%79.4%None
Wayne CountyZone 3100%NoneNone
Wilson CountyZone 3100%NoneNone
Harnett CountyZone 388.1%11.9%None
Nash CountyZone 386.8%13.2%None
Franklin CountyZone 20.2%99.8%None
Sampson CountyZone 3100%NoneNone
North Carolina100 counties, pooled by land areaVaries64.8%33.0%1.3%

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

Local help

Johnston County, Local resources

Radon testing and mitigation in Johnston County

What North Carolina's program says
Licensing of radon professionals
The North Carolina Radon Program is presently developing a Radon Proficiency Program as directed by Session Law 2023-91 House Bill 782 .

What it means

Johnston County, Questions

Questions about radon in Johnston County

Are radon levels high in Johnston County?

In 2022, 0.0% of the radon tests reported to CDC for Johnston County, North Carolina were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.1 pCi/L. Of 75 North Carolina counties with 30 or more tests for the same period, 55 reported a higher share; pooled, the state comes to 22.6%.

Which counties border Johnston County?

Johnston County borders 7 counties: Wake County, Wayne County, Wilson County, Harnett County, Nash County, Franklin County and Sampson County.

Products

Johnston County, Products

Testing a home in Johnston County

In Johnston County, 8.2% of 668 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 22.6% pooled across North Carolina. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Johnston County.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Johnston County homes, compared

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Johnston County, Bordering counties

Counties bordering Johnston County

Calculated by Radon411

Johnston County, Cities and towns

Cities and towns in Johnston County

Johnston County is growing: the Census Bureau puts it at 256,448 residents on July 1, 2025, up 17.9% from 217,450 in 2020. That works out to 324 people per square mile of land. Clayton, the largest place on its list (32,633 residents in all), extends beyond Johnston County, so no share of the total is worked out for it. Reported testing is thin here: 668 tests over 2008 to 2017, or 2.6 for every 1,000 residents (2025 estimate), where North Carolina as a whole comes to 6.5.

From Clayton to Micro, CDC publishes no figure by town: each reads Johnston County's.

The cities and towns in Johnston County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Claytonextends beyond Johnston County32,633+22.3%Counted whole
Smithfield13,114+15.2%5.1%
Zebulonextends beyond Johnston County11,933+69.6%Counted whole
Selma7,406+16.4%2.9%
Archer Lodge5,649+17.2%2.2%
Bensonextends beyond Johnston County4,660+16.3%Counted whole
Wilson's Mills2,987+16.9%1.2%
Four Oaks2,978+31.3%1.2%
Pine Level2,405+16.3%0.9%
Kenlyextends beyond Johnston County1,722+14.8%Counted whole
Princeton1,544+16.8%0.6%
Micro537+17.2%0.2%

12 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 Johnston County is counted whole, so it has no share.

Johnston County, Homes

Homes in Johnston County

Johnston County is a place of houses on their own lots: 75% of its 88,314 homes are detached single-family houses, against 65% across North Carolina. Much of Johnston County is recent building: 47% of its homes have gone up since 2000 and the middle year built is 1999, against 1990 for North Carolina. Owners live in 77% of the occupied homes (North Carolina: 66%), so for most households a test and a fix are their own to order.

Homes in Johnston County, North Carolina, 2019 to 2023
HomesJohnston CountyNorth Carolina
Housing units88,3144,815,195
Detached houses75%65%
In buildings of 5 or more5%14%
Mobile homes14%11%
Built before 196011%14%
Built since 200047%33%
Middle year built19991990
Owner-occupied77%66%

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