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Radon Levels in Gillespie County, Texas

EPA puts Gillespie County in Zone 3, its lowest radon zone, and only 6 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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  • Nearest county

    6.6%

    Bexar County, 65 miles

    Bexar
    6.6%
    Texas
    10.4%

    Share at 4+ pCi/L, 197 tests, 2007 to 2016

  • Ground above low

    13.2%

    14.1 pts below Texas

    Gillespie
    13.2%
    Texas
    27.3%

    Share of land USGS rates moderate or high potential

  • Tests reported

    11

    Too few for a share

    Gillespie
    11
    Needed
    30

    2006 to 2015, 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 Gillespie 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

Gillespie County, At a glance

Gillespie County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Gillespie 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 87% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

CDC holds 6 reported tests for Gillespie County over the 2008 to 2017 laboratory totals, with a median of 0.6 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Gillespie County beside the counties around it is how this page reads it.

What these figures count

Only 6 tests were reported to CDC for Gillespie 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

Gillespie County, Compared

Gillespie County radon figures, compared

Calculated by Radon411

CDC's largest figure for Gillespie County rests on 11 tests over the 2006 to 2015 laboratory totals, 2 of them at or above 4 pCi/L, so each test moves its share by 9.1 points and no rank or comparison is drawn from it. Results reached as high as 4.7 pCi/L, with a middle value of 1.0 pCi/L.

The nearest counties with a figure are Bexar County (65 miles away) at 6.6%, Travis County (70 miles away) at 9.3% and Williamson County (83 miles away) at 2.0%. 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 Gillespie County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 87% of the county's land low radon potential.

Texas, the United States and the counties around Gillespie 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
Kendall County, TXborders it771.4%5.7 pCi/L
Kerr County, TXborders it1612.5%1.1 pCi/L
Kimble County, TXborders it10.0%2.1 pCi/L
Blanco County, TXborders it20.0%0.2 pCi/L
Llano County, TXborders it60.0%1.5 pCi/L
The nearest Texas counties to Gillespie County with 30 or more tests, 2007 to 2016, laboratory
CountyDistanceTestsAt or above 4 pCi/LMedian
Bexar County65 mi1976.6%0.6 pCi/L
Travis County70 mi4089.3%0.8 pCi/L
Williamson County83 mi982.0%0.7 pCi/L
Bell County101 mi3514.3%1.1 pCi/L
McLennan County134 mi4117.1%1.0 pCi/L
Brazos County159 mi490.0%0.2 pCi/L
Tarrant County195 mi31210.6%0.9 pCi/L
Nueces County196 mi450.0%0.6 pCi/L
Gillespie County ten-year laboratory totals, against Texas' pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestTexas, pooledChange from the row before
2008 to 2017616.7%0.6 pCi/L37.3 pCi/L10.2%−3.3 points
2007 to 20161020.0%0.8 pCi/L4.7 pCi/L10.4%+1.8 points
2006 to 20151118.2%1.0 pCi/L4.7 pCi/L11.0%−1.8 points
2005 to 20141020.0%1.3 pCi/L4.7 pCi/L10.6%First on file

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

Gillespie County, Geology

The ground under Gillespie County

Predicted

Most of the ground under Gillespie County is one class on USGS's geologic map: 86.8% of its land is low radon potential, with 13.2% moderate. The map puts 86.8% of Gillespie County in the area it calls Southern High Plains and Plateaus and 13.2% in Llano Uplift. USGS gives the first a radon index of 7, in the low band (5 to 8), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Gillespie County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Southern High Plains and PlateausPaleozoic and Mesozoic sandstone, limestone, shale.Low786.8%
Llano UpliftPrecambrian metamorphic and undifferentiated igneous rocks.Moderate1013.2%

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

Gillespie County beside the ground around it

Across Texas 0.5% of the land is rated high; none of Gillespie County's is. Of the 6 counties that border it, 3 have more moderate-potential ground, Llano County the most at 100%.

Share of land by USGS radon potential: Gillespie County, the 6 counties bordering it and Texas
AreaEPA zoneLow potentialModerate potentialHigh potential
Gillespie CountyZone 386.8%13.2%None
Llano CountyZone 2None100%None
Mason CountyZone 214.3%85.7%None
Blanco CountyZone 364.7%35.3%None
Kerr CountyZone 3100%NoneNone
Kendall CountyZone 3100%NoneNone
Kimble CountyZone 398.3%1.7%None
Texas254 counties, pooled by land areaVaries72.4%26.8%0.5%

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

Local help

Gillespie County, Local resources

Radon testing and mitigation in Gillespie 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

Gillespie County, Questions

Questions about radon in Gillespie County

Are radon levels high in Gillespie County?

Over the 2008 to 2017 laboratory totals, 16.7% of the radon tests reported to CDC for Gillespie County, Texas were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.6 pCi/L. Of the 8 nearest counties with a figure, within 196 miles, the share of tests at or above 4 pCi/L runs from 0.0% to 17.1%.

Which counties border Gillespie County?

Gillespie County borders 6 counties: Llano County, Mason County, Blanco County, Kerr County, Kendall County and Kimble County.

Products

Gillespie County, Products

Testing a home in Gillespie County

No CDC figure names Gillespie County; the nearest county with one, Bexar County (65 miles away), reported 6.6% 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 Gillespie County.

Test kits and monitors3

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Best radon monitors for Gillespie County homes, compared

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Gillespie County, Bordering counties

Counties bordering Gillespie County

Calculated by Radon411

Gillespie County, Cities and towns

Cities and towns in Gillespie County

Gillespie County is growing: the Census Bureau puts it at 28,527 residents on July 1, 2025, up 6.6% from 26,768 in 2020. That works out to 27 people per square mile of land. Fredericksburg, its one incorporated place, has 11,893 residents, 41.7% of the total. Testing is reported here more often than across the state: CDC's 11 reported tests for 2006 to 2015 come to 0.4 for every 1,000 residents (2025 estimate), against 0.1 for Texas.

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

Fredericksburg, Gillespie County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Fredericksburg11,893+7.9%41.7%

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).

Gillespie County, Homes

Homes in Gillespie County

Of Gillespie County's 14,255 homes, 75% are detached houses, against 65% across Texas; 12% are mobile homes. Half of its homes were built before 1991, close to Texas' 1990: 18% date from before 1960 and 35% from 2000 or later. 71% 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 Gillespie County, Texas, 2019 to 2023
HomesGillespie CountyTexas
Housing units14,25511,890,808
Detached houses75%65%
In buildings of 5 or more6%21%
Mobile homes12%7%
Built before 196018%13%
Built since 200035%37%
Middle year built19911990
Owner-occupied71%63%

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