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Radon Levels in Bexar County, Texas

EPA puts Bexar County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 6.5% of 201 (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

    6.5%

    3.7 pts below TX

    Bexar
    6.5%
    Texas
    10.2%

    201 tests, 2008 to 2017

  • Median result

    0.6pCi/L

    Below action level

    Bexar
    0.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    201

    6th of 22 by tests

    Bexar
    201
    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

    11 of 22

    Middle half

    Bexar
    6.5%
    Randall
    69.0%

    By share, of 22 with 30+ tests

Read a result for Bexar County

Starts at Bexar County's median, 0.6 pCi/L

0.6pCi/L

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

EPA’s reading of 0.6 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. Bexar County's median reported result, 2008 to 2017.

Interpret this reading

The data

Bexar County, At a glance

Bexar County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Bexar 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 Bexar County, 2008 to 2017, laboratory

Reported results by concentration band, Bexar County, 2008 to 2017, laboratory
Under 2 pCi/L: 87%2 to 4 pCi/L: 7%4 pCi/L and above: 6%

Of 201 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Bexar County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L17587.1%
2 to 4 pCi/L136.5%
4 pCi/L and above136.5%
What these figures count

These are the 201 tests reported to CDC for Bexar 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

Bexar County, Compared

Bexar County radon figures, compared

Calculated by Radon411

Bexar County reports fewer high tests than Texas overall. 6.5% of its 201 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 3.7 points below the 10.2% pooled from 138 Texas counties.

Ordered from highest share down, it comes 11th of 22 Texas counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; Bexar County sits 29.2 points below it.

Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 6.5% share point the same way here.

Half the tests came in under 0.6 pCi/L and half over it; the single highest reached 9.8 pCi/L. The rest split 87.1% under 2 pCi/L and 6.5% from 2 to 4 (Texas: 80.3% and 9.6%).

CDC's ten-year totals for Bexar County went from 156 tests (2005 to 2014) to 201 (2008 to 2017), the share going from 4.5% to 6.5%.

Bexar County against Texas, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Bexar County
Bexar County2016.5%0.6 pCi/LThis county
Texas, pooled138 counties, pooled4,61510.2%Not pooled+3.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+29.2 points
Randall Countyhighest in the state8769.0%6.1 pCi/L+62.5 points
Nueces Countylowest in the state430.0%0.6 pCi/L−6.5 points
Kendall County, TXborders it771.4%5.7 pCi/L+64.9 points
Comal County, TXborders it224.5%0.9 pCi/L−2.0 points
Atascosa County, TXborders it10.0%1.1 pCi/L−6.5 points
Wilson County, TXborders it10.0%0.1 pCi/L−6.5 points
Medina County, TXborders it20.0%0.5 pCi/L−6.5 points
Guadalupe County, TXborders it30.0%0.6 pCi/L−6.5 points
Where Bexar County's reported results fell, 2008 to 2017, laboratory, beside Texas and the United States
ResultBexar County testsBexar County shareTexas shareU.S. shareAgainst Texas
Under 2 pCi/L17587.1%80.3%39.6%+6.8 points
2 to 4 pCi/L136.5%9.6%24.7%−3.1 points
4 pCi/L and above136.5%10.2%35.7%−3.7 points
Bexar 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
Tarrant County6 of 2228413.0%0.9 pCi/L
Travis County7 of 224269.2%0.9 pCi/L
Dallas County8 of 227288.4%0.9 pCi/L
Collin County9 of 222897.6%1.0 pCi/L
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
Bexar County ten-year laboratory totals, against Texas' pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestTexas, pooledChange from the row before
2008 to 20172016.5%0.6 pCi/L9.8 pCi/L10.2%−0.1 points
2007 to 20161976.6%0.6 pCi/L9.8 pCi/L10.4%+2.3 points
2006 to 20151634.3%0.5 pCi/L8.9 pCi/L11.0%−0.2 points
2005 to 20141564.5%0.6 pCi/L8.9 pCi/L10.6%First on file

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

Bexar County, Geology

The ground under Bexar County

Predicted

USGS's geologic map puts all of Bexar County's mapped land in one class: low radon potential. The map puts 79.3% of Bexar County in the area it calls East Texas Province and 20.7% in Southern High Plains and Plateaus. USGS gives the first a radon index of 6 and the second 7, both in the low band (5 to 8).

USGS's geologic areas under Bexar County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
East Texas ProvinceCretaceous through Quaternary marine sandstone, shale, chalk, limestone, siltstone, clay, and lignite.Low679.3%
Southern High Plains and PlateausPaleozoic and Mesozoic sandstone, limestone, shale.Low720.7%

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

Bexar County beside the ground around it

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

Share of land by USGS radon potential: Bexar County, the 7 counties bordering it and Texas
AreaEPA zoneLow potentialModerate potentialHigh potential
Bexar CountyZone 3100%NoneNone
Atascosa CountyZone 3100%NoneNone
Wilson CountyZone 3100%NoneNone
Comal CountyZone 3100%NoneNone
Medina CountyZone 3100%NoneNone
Kendall CountyZone 3100%NoneNone
Guadalupe CountyZone 3100%NoneNone
Bandera 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

Bexar County, Local resources

Radon testing and mitigation in Bexar 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

Bexar County, Questions

Questions about radon in Bexar County

Are radon levels high in Bexar County?

Over the 2008 to 2017 laboratory totals, 6.5% of the radon tests reported to CDC for Bexar County, Texas were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.6 pCi/L. Of 22 Texas counties with 30 or more tests for the same period, 10 reported a higher share; pooled, the state comes to 10.2%.

Which counties border Bexar County?

Bexar County borders 7 counties: Atascosa County, Wilson County, Comal County, Medina County, Kendall County, Guadalupe County and Bandera County.

Products

Bexar County, Products

Testing a home in Bexar County

In Bexar County, 6.5% of 201 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 Bexar County.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Bexar County homes, compared

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Bexar County, Bordering counties

Counties bordering Bexar County

Calculated by Radon411

Bexar County, Cities and towns

Cities and towns in Bexar County

Bexar County is growing: the Census Bureau puts it at 2,160,088 residents on July 1, 2025, up 7.2% from 2,015,492 in 2020. Packed into its land, that is 1,742 people per square mile. San Antonio, the largest place on its list (1,548,422 residents in all), extends beyond Bexar County, so no share of the total is worked out for it. Reported testing is thin here: 201 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 San Antonio to Grey Forest, CDC publishes no figure by town: each reads Bexar County's.

The 12 largest cities and towns in Bexar County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
San Antonioextends beyond Bexar County1,548,422+7.7%Counted whole
Schertzextends beyond Bexar County45,978+8.8%Counted whole
Ciboloextends beyond Bexar County39,019+18.9%Counted whole
Converse32,481+16.6%1.5%
Universal City20,399+3.3%0.9%
Live Oak16,426+3.8%0.8%
Fair Oaks Ranchextends beyond Bexar County12,025+21.0%Counted whole
Selmaextends beyond Bexar County11,955+4.6%Counted whole
Leon Valley11,563+0.1%0.5%
Helotes10,387+15.1%0.5%
Kirby8,211+0.7%0.4%
Alamo Heights7,632+3.4%0.4%
  • Sandy Oaks
  • Windcrest
  • Terrell Hills
  • Castle Hills
  • Shavano Park
  • Lytle (part)
  • Hollywood Park
  • Elmendorf (part)
  • Balcones Heights
  • St. Hedwig
  • Olmos Park
  • Somerset
  • Von Ormy
  • China Grove
  • Hill Country Village
  • Grey Forest

28 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 Bexar County is counted whole, so it has no share.

Bexar County, Homes

Homes in Bexar County

Of Bexar County's 807,160 homes, 65% are detached houses, against 65% across Texas; 24% are in buildings of five or more homes. Half of its homes were built before 1989, close to Texas' 1990: 16% date from before 1960 and 37% from 2000 or later. 59% 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 Bexar County, Texas, 2019 to 2023
HomesBexar CountyTexas
Housing units807,16011,890,808
Detached houses65%65%
In buildings of 5 or more24%21%
Mobile homes3%7%
Built before 196016%13%
Built since 200037%37%
Middle year built19891990
Owner-occupied59%63%

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