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Radon Levels in Johnson County, Texas

EPA puts Johnson County in Zone 3, its lowest radon zone, and only 14 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Highest bordering

    10.6%

    Tarrant County

    Tarrant
    10.6%

    1 of 7 neighbours have 30+ tests, 2007 to 2016

  • Nearest county

    10.6%

    Tarrant County, 27 miles

    Tarrant
    10.6%
    Texas
    10.4%

    Share at 4+ pCi/L, 312 tests, 2007 to 2016

  • Ground above low

    54.0%

    26.7 pts above Texas

    Johnson
    54.0%
    Texas
    27.3%

    Share of land USGS rates moderate or high potential

  • Tests reported

    14

    Too few for a share

    Johnson
    14
    Needed
    30

    2008 to 2017, laboratory

  • 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

Read a result for Johnson County

Starts at EPA's action level

4.0pCi/L

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

EPA’s reading of 4.0 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.

Interpret this readingWhat a fix costs

The data

Johnson County, At a glance

Johnson County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Johnson 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: Moderate across 54% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

CDC holds 14 reported tests for Johnson County over the 2008 to 2017 laboratory totals, with a median of 0.8 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Johnson County beside the counties around it is how this page reads it.

What these figures count

Only 14 tests were reported to CDC for Johnson County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Johnson County, Compared

Johnson County radon figures, compared

Calculated by Radon411

CDC's largest figure for Johnson County rests on 14 tests over the 2008 to 2017 laboratory totals, 0 of them at or above 4 pCi/L, so each test moves its share by 7.1 points and no rank or comparison is drawn from it. Results reached as high as 2.2 pCi/L, with a middle value of 0.8 pCi/L.

Tarrant County, the one bordering county with a figure over the 2007 to 2016 laboratory totals, reported 10.6% of its tests at or above 4 pCi/L. Farther out, Dallas County (44 miles away) at 8.7%, McLennan County (58 miles away) at 17.1% and Denton County (59 miles away) at 7.2% have figures too. Pooled across 140 Texas counties, 10.4% of reported tests reached that level; across every county in the country with a figure, 35.8%.

Statewide for the same period, Randall County reported the highest share (71.4%) and Nueces County the lowest (0.0%). EPA's 1993 map puts Johnson County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 54% of the county's land moderate radon potential.

Texas, the United States and the counties around Johnson County, 2007 to 2016, laboratory
AreaTestsAt or above 4 pCi/LMedian
Texas, pooled140 counties, pooled4,54810.4%Not pooled
United States, pooled2,666 counties, pooled1,939,02535.8%Not pooled
Randall Countyhighest in the state8471.4%6.2 pCi/L
Nueces Countylowest in the state450.0%0.6 pCi/L
Ellis County, TXborders it1457.1%11.0 pCi/L
Tarrant County, TXborders it31210.6%0.9 pCi/L
Parker County, TXborders it2010.0%1.0 pCi/L
Hood County, TXborders it50.0%0.7 pCi/L
Hill County, TXborders it50.0%0.1 pCi/L
The nearest Texas counties to Johnson County with 30 or more tests, 2007 to 2016, laboratory
CountyDistanceTestsAt or above 4 pCi/LMedian
Tarrant County27 mi31210.6%0.9 pCi/L
Dallas County44 mi6998.7%1.0 pCi/L
McLennan County58 mi4117.1%1.0 pCi/L
Denton County59 mi1817.2%0.9 pCi/L
Collin County72 mi2847.7%1.0 pCi/L
Bell County93 mi3514.3%1.1 pCi/L
Williamson County120 mi982.0%0.7 pCi/L
Smith County123 mi339.1%0.8 pCi/L
Johnson County ten-year laboratory totals, against Texas' pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestTexas, pooledChange from the row before
2008 to 2017140.0%0.8 pCi/L2.2 pCi/L10.2%Level
2007 to 2016140.0%0.8 pCi/L2.2 pCi/L10.4%Level
2006 to 2015130.0%0.6 pCi/L2.1 pCi/L11.0%Level
2005 to 201470.0%0.9 pCi/L2.1 pCi/L10.6%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

USGS's geologic map splits Johnson County: 54.0% of its land is moderate radon potential and 46.0% low. The map puts 54.0% of Johnson County in the area it calls Cretaceous Gulfian series and 46.0% in Central Texas/Gulf Coast Plain. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 7, in the low band (5 to 8).

USGS's geologic areas under Johnson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Cretaceous Gulfian seriesCretaceous sandstone, shale, limestone, siltstone.Moderate1054.0%
Central Texas/Gulf Coast PlainCretaceous through Quaternary marine sandstone, shale, chalk, limestone, siltstone, clay, and lignite.Low746.0%

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

Across Texas 0.5% of the land is rated high; none of Johnson County's is. Of the 7 counties that border it, 1 has more moderate-potential ground, Hill County the most at 54.9%.

Share of land by USGS radon potential: Johnson County, the 7 counties bordering it and Texas
AreaEPA zoneLow potentialModerate potentialHigh potential
Johnson CountyZone 346.0%54.0%None
Tarrant CountyZone 357.5%42.5%None
Hood CountyZone 3100%NoneNone
Hill CountyZone 345.1%54.9%None
Somervell CountyZone 3100%NoneNone
Ellis CountyZone 358.7%41.3%None
Parker CountyZone 3100%NoneNone
Bosque CountyZone 3100%NoneNone
Texas254 counties, pooled by land areaVaries72.4%26.8%0.5%

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 Texas's program says
Licensing of radon professionals
There are no radon certification requirements for the State of Texas at this time, but the National Radon Proficiency Program lists radon testers and mitigators within Texas that have passed a rigorous national certification program.

What it means

Johnson County, Questions

Questions about radon in Johnson County

Are radon levels high in Johnson County?

Over the 2008 to 2017 laboratory totals, 0.0% of the radon tests reported to CDC for Johnson County, Texas were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.8 pCi/L. Tarrant County, the one bordering county with a figure over the 2007 to 2016 laboratory totals, reported 10.6% of its tests at or above 4 pCi/L.

Which counties border Johnson County?

Johnson County borders 7 counties: Tarrant County, Hood County, Hill County, Somervell County, Ellis County, Parker County and Bosque County.

Products

Johnson County, Products

Testing a home in Johnson County

No CDC figure names Johnson County; the nearest county with one, Tarrant County (27 miles away), reported 10.6% of its tests at or above 4 pCi/L over the 2007 to 2016 laboratory totals, the only reading nearby until a test of this home. 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 Johnson County.

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

Johnson County is growing: the Census Bureau puts it at 218,048 residents on July 1, 2025, up 20.5% from 180,955 in 2020. That works out to 301 people per square mile of land. Fort Worth, the largest place on its list (1,028,117 residents in all), extends beyond Johnson County, so no share of the total is worked out for it. Reported testing is thin here: 14 tests over 2008 to 2017, or 0.1 for every 1,000 residents (2025 estimate), where Texas as a whole comes to 0.1.

From Fort Worth to Coyote Flats, CDC publishes no figure by town: each reads Johnson County's.

The 12 largest cities and towns in Johnson County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Fort Worthextends beyond Johnson County1,028,117+11.3%Counted whole
Mansfieldextends beyond Johnson County84,444+16.0%Counted whole
Burlesonextends beyond Johnson County56,907+18.6%Counted whole
Cleburne39,942+27.0%18.3%
Crowleyextends beyond Johnson County20,954+14.2%Counted whole
Joshua9,352+17.8%4.3%
Venusextends beyond Johnson County8,870+93.3%Counted whole
Alvarado7,539+40.3%3.5%
Keene7,109+10.4%3.3%
Godley5,093+235.5%2.3%
Cressonextends beyond Johnson County2,126+47.5%Counted whole
Grandview2,090+11.6%1.0%
  • Rio Vista
  • Briaroaks
  • Cross Timber
  • Coyote Flats

16 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 Johnson County is counted whole, so it has no share.

Johnson County, Homes

Homes in Johnson County

Of Johnson County's 68,594 homes, 69% are detached houses, against 65% across Texas; 18% are mobile homes. Half of its homes were built before 1995, close to Texas' 1990: 8% date from before 1960 and 42% from 2000 or later. 74% of occupied homes are lived in by their owner (Texas: 63%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Johnson County, Texas, 2019 to 2023
HomesJohnson CountyTexas
Housing units68,59411,890,808
Detached houses69%65%
In buildings of 5 or more6%21%
Mobile homes18%7%
Built before 19608%13%
Built since 200042%37%
Middle year built19951990
Owner-occupied74%63%

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