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Radon Levels in Harris County, Texas

EPA puts Harris County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 2.9% of 733 (2008 to 2017, laboratory totals) reached 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

    2.9%

    7.3 pts below TX

    Harris
    2.9%
    Texas
    10.2%

    733 tests, 2008 to 2017

  • Median result

    0.4pCi/L

    Below action level

    Harris
    0.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    733

    Most tested in Texas

    Harris
    733

    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 Texas

    15 of 22

    Middle half

    Harris
    2.9%
    Randall
    69.0%

    By share, of 22 with 30+ tests

Read a result for Harris County

Starts at Harris County's median, 0.4 pCi/L

0.4pCi/L

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

EPA’s reading of 0.4 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. Harris County's median reported result, 2008 to 2017.

Interpret this reading

The data

Harris County, At a glance

Harris County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Harris 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Harris County, 2008 to 2017, laboratory
Under 2 pCi/L: 95%2 to 4 pCi/L: 2%4 pCi/L and above: 3%

Of 733 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Harris County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L69895.2%
2 to 4 pCi/L141.9%
4 pCi/L and above212.9%
What these figures count

These are the 733 tests reported to CDC for Harris 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

Harris County, Compared

Harris County radon figures, compared

Calculated by Radon411

Only 21 of 733 radon tests reported for Harris County over the 2008 to 2017 laboratory totals reached 4 pCi/L (2.9%). The median result, 0.4 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 46.3 pCi/L.

Across 138 Texas counties pooled together, 10.2% of tests reached that level, so Harris County runs 7.3 points below its state. Against the national pool of 35.7%, the gap is 32.8 points lower. Its place in the state: 15th of 22 Texas counties with 30 or more tests for the same period.

Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 2.9% share point the same way here. Of 4 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 0.0% (Galveston County) to 6.3% (Brazoria County).

Below the action level, 698 tests (95.2%) came in under 2 pCi/L, against 80.3% statewide, and 14 tests (1.9%) fell between 2 and 4, against 9.6% statewide. USGS geology rates 100% of the county's land low radon potential.

CDC's ten-year totals for Harris County went from 647 tests (2005 to 2014) to 733 (2008 to 2017), the share going from 3.9% to 2.9%.

Harris County against Texas, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Harris County
Harris County7332.9%0.4 pCi/LThis county
Texas, pooled138 counties, pooled4,61510.2%Not pooled+7.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+32.8 points
Randall Countyhighest in the state8769.0%6.1 pCi/L+66.1 points
Nueces Countylowest in the state430.0%0.6 pCi/L−2.9 points
Brazoria County, TXborders it326.3%0.3 pCi/L+3.4 points
Montgomery County, TXborders it1883.2%0.8 pCi/L+0.3 points
Fort Bend County, TXborders it1052.9%0.2 pCi/LLevel
Chambers County, TXborders it30.0%0.1 pCi/L−2.9 points
Liberty County, TXborders it10.0%1.2 pCi/L−2.9 points
Waller County, TXborders it70.0%0.1 pCi/L−2.9 points
Galveston County, TXborders it730.0%0.2 pCi/L−2.9 points
Where Harris County's reported results fell, 2008 to 2017, laboratory, beside Texas and the United States
ResultHarris County testsHarris County shareTexas shareU.S. shareAgainst Texas
Under 2 pCi/L69895.2%80.3%39.6%+14.9 points
2 to 4 pCi/L141.9%9.6%24.7%−7.7 points
4 pCi/L and above212.9%10.2%35.7%−7.3 points
Harris County ranked among the 22 Texas counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Denton County10 of 221926.8%0.9 pCi/L
Bexar County11 of 222016.5%0.6 pCi/L
Brazoria County12 of 22326.3%0.3 pCi/L
Smith County13 of 22525.8%0.8 pCi/L
Montgomery County14 of 221883.2%0.8 pCi/L
Harris County15 of 227332.9%0.4 pCi/L
Fort Bend County16 of 221052.9%0.2 pCi/L
Williamson County17 of 221031.9%0.7 pCi/L
Midland County18 of 221001.0%0.7 pCi/L
Galveston County19 of 22730.0%0.2 pCi/L
El Paso County19 of 22570.0%0.7 pCi/L
Harris County ten-year laboratory totals, against Texas' pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestTexas, pooledChange from the row before
2008 to 20177332.9%0.4 pCi/L46.3 pCi/L10.2%−0.2 points
2007 to 20167753.1%0.2 pCi/L46.3 pCi/L10.4%−0.9 points
2006 to 20156684.0%0.2 pCi/L46.3 pCi/L11.0%+0.1 points
2005 to 20146473.9%0.2 pCi/L46.3 pCi/L10.6%First on file

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

Harris County, Geology

The ground under Harris County

Predicted

USGS's geologic map puts all of Harris County's mapped land in one class: low radon potential. All of it lies in the area the map calls Coastal Plain, to which USGS gives a radon index of 7, in the low band (5 to 8).

USGS's geologic areas under Harris County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Coastal PlainCretaceous through Quaternary marine sandstone, shale, chalk, limestone, siltstone, clay, and lignite.Low7100%

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

Harris County beside the ground around it

Across Texas 0.5% of the land is rated high; none of Harris County's is. None of the 7 counties that border it has any moderate-potential ground either.

Share of land by USGS radon potential: Harris County, the 7 counties bordering it and Texas
AreaEPA zoneLow potentialModerate potentialHigh potential
Harris CountyZone 3100%NoneNone
Fort Bend CountyZone 3100%NoneNone
Montgomery CountyZone 3100%NoneNone
Galveston CountyZone 384.4%NoneNone
Waller CountyZone 3100%NoneNone
Liberty CountyZone 3100%NoneNone
Brazoria CountyZone 398.0%NoneNone
Chambers CountyZone 398.3%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

Harris County, Local resources

Radon testing and mitigation in Harris County

Listed radon professionals by town: Houston

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

Harris County, Questions

Questions about radon in Harris County

Are radon levels high in Harris County?

Over the 2008 to 2017 laboratory totals, 2.9% of the radon tests reported to CDC for Harris County, Texas were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.4 pCi/L. Of 22 Texas counties with 30 or more tests for the same period, 14 reported a higher share; pooled, the state comes to 10.2%.

Which counties border Harris County?

Harris County borders 7 counties: Fort Bend County, Montgomery County, Galveston County, Waller County, Liberty County, Brazoria County and Chambers County.

Products

Harris County, Products

Testing a home in Harris County

In Harris County, 2.9% of 733 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.2% pooled across Texas. 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 Harris County.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Harris County homes, compared

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Harris County, Bordering counties

Counties bordering Harris County

Calculated by Radon411

Harris County, Cities and towns

Cities and towns in Harris County

Harris County is growing: the Census Bureau puts it at 5,045,026 residents on July 1, 2025, up 6.6% from 4,734,060 in 2020. Packed into its land, that is 2,956 people per square mile. Houston, the largest place on its list (2,397,315 residents in all), extends beyond Harris County, so no share of the total is worked out for it. CDC's 733 reported tests for 2008 to 2017 work out to 0.1 per 1,000 residents (2025 estimate), close to Texas' 0.1.

From Houston to Morgan's Point, CDC publishes no figure by town: each reads Harris County's.

The 12 largest cities and towns in Harris County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Houstonextends beyond Harris County2,397,315+4.3%Counted whole
Pasadena148,539−1.9%2.9%
Pearlandextends beyond Harris County129,930+1.7%Counted whole
League Cityextends beyond Harris County119,905+4.6%Counted whole
Baytownextends beyond Harris County86,561+1.4%Counted whole
Missouri Cityextends beyond Harris County77,327+3.9%Counted whole
Friendswoodextends beyond Harris County41,319+0.7%Counted whole
La Porte37,983+7.6%0.8%
Deer Park34,282−0.3%0.7%
Katyextends beyond Harris County28,373+26.5%Counted whole
Staffordextends beyond Harris County18,043+3.8%Counted whole
Bellaire17,434+1.4%0.3%
  • Humble
  • South Houston
  • Tomball (part)
  • West University Place
  • Seabrook (part)
  • Webster
  • Galena Park
  • Jacinto City
  • Jersey Village
  • Waller (part)
  • Nassau Bay
  • Hunters Creek Village
  • Spring Valley Village
  • Bunker Hill Village
  • Taylor Lake Village
  • Piney Point Village
  • El Lago
  • Hedwig Village
  • Southside Place
  • Shoreacres (part)
  • Hilshire Village
  • Morgan's Point (part)

34 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 Harris County is counted whole, so it has no share.

Harris County, Homes

Homes in Harris County

Of Harris County's 1,884,607 homes, 57% are detached houses, against 65% across Texas; 32% are in buildings of five or more homes. Half of its homes were built before 1988, close to Texas' 1990: 12% date from before 1960 and 35% from 2000 or later. 55% 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 Harris County, Texas, 2019 to 2023
HomesHarris CountyTexas
Housing units1,884,60711,890,808
Detached houses57%65%
In buildings of 5 or more32%21%
Mobile homes3%7%
Built before 196012%13%
Built since 200035%37%
Middle year built19881990
Owner-occupied55%63%

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