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Radon Levels in Fresno County, California

EPA puts Fresno County in Zone 2, its middle radon zone, and most reported tests there come back low, though 11.0% of 100 (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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    11.0%

    0.7 pts above CA

    Fresno
    11.0%
    California
    10.3%

    100 tests, 2008 to 2017

  • Median result

    1.5pCi/L

    Below action level

    Fresno
    1.5 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    100

    20th of 33 by tests

    Fresno
    100
    Los Angeles
    2,363

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in California

    17 of 33

    Middle half

    Fresno
    11.0%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for Fresno County

Starts at Fresno County's median, 1.5 pCi/L

1.5pCi/L

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

EPA’s reading of 1.5 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. Fresno County's median reported result, 2008 to 2017.

Interpret this reading

The data

Fresno County, At a glance

Fresno County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Fresno County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 61% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Fresno County, 2008 to 2017, laboratory
Under 2 pCi/L: 65%2 to 4 pCi/L: 24%4 pCi/L and above: 11%

Of 100 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Fresno County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L6565.0%
2 to 4 pCi/L2424.0%
4 pCi/L and above1111.0%
What these figures count

These are the 100 tests reported to CDC for Fresno 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

Fresno County, Compared

Fresno County radon figures, compared

Calculated by Radon411

11.0% of its 100 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 0.7 points above the 10.3% pooled from 56 California counties.

Ordered from highest share down, it comes 17th of 33 California counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; Fresno County sits 24.7 points below it.

Next door, the shares run from 14.7% in Madera County to 23.8% in Tulare County. Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 11.0% share point the same way here.

Half the tests came in under 1.5 pCi/L and half over it; the single highest reached 14.8 pCi/L. The rest split 65.0% under 2 pCi/L and 24.0% from 2 to 4 (California: 76.8% and 12.9%).

CDC's ten-year totals for Fresno County went from 96 tests (2005 to 2014) to 100 (2008 to 2017), the share going from 10.4% to 11.0%.

Fresno County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Fresno County
Fresno County10011.0%1.5 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled−0.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+24.7 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+19.3 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−10.2 points
Inyo County, CAborders it1450.0%4.0 pCi/L+39.0 points
Mono County, CAborders it2050.0%4.6 pCi/L+39.0 points
Tulare County, CAborders it8023.8%1.7 pCi/L+12.8 points
Monterey County, CAborders it8714.9%0.8 pCi/L+3.9 points
Madera County, CAborders it3414.7%1.4 pCi/L+3.7 points
San Benito County, CAborders it190.0%0.7 pCi/L−11.0 points
Kings County, CAborders it20.0%1.7 pCi/L−11.0 points
Merced County, CAborders it50.0%2.1 pCi/L−11.0 points
Where Fresno County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultFresno County testsFresno County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L6565.0%76.8%39.6%−11.8 points
2 to 4 pCi/L2424.0%12.9%24.7%+11.1 points
4 pCi/L and above1111.0%10.3%35.7%+0.7 points
Fresno County ranked among the 33 California counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Madera County12 of 333414.7%1.4 pCi/L
San Luis Obispo County13 of 338012.5%1.0 pCi/L
Ventura County14 of 3333511.9%1.0 pCi/L
Kern County15 of 3312111.6%1.8 pCi/L
Butte County16 of 333511.4%0.8 pCi/L
Fresno County17 of 3310011.0%1.5 pCi/L
Napa County18 of 335710.5%0.9 pCi/L
Los Angeles County19 of 332,3639.5%0.7 pCi/L
Santa Clara County20 of 337939.2%0.9 pCi/L
San Mateo County21 of 334689.2%0.9 pCi/L
Contra Costa County22 of 332858.8%0.9 pCi/L
Fresno County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 201710011.0%1.5 pCi/L14.8 pCi/L10.3%−2.0 points
2007 to 201610813.0%1.6 pCi/L14.8 pCi/L10.6%+1.2 points
2006 to 20159311.8%1.6 pCi/L14.8 pCi/L10.6%+1.4 points
2005 to 20149610.4%1.6 pCi/L14.8 pCi/L10.0%First on file

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

Fresno County, Geology

The ground under Fresno County

Predicted

USGS's geologic map splits Fresno County: 61.4% of its land is moderate radon potential and 38.6% low. The map puts 45.7% of Fresno County in the area it calls Sierra Nevada and 38.6% in Great Valley, with one smaller area beside them. USGS gives the first a radon index of 9, in the moderate band (9 to 11), and the second 8, in the low band (5 to 8).

USGS's geologic areas under Fresno County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Sierra NevadaNorthern Sierra Nevada is underlain primarily by Paleozoic and Mesozoic metamorphic rocks. Granitic rocks predominate in the southern Sierrra Nevada , with lesser Mesozoic metamorphic rocks.Moderate945.7%
Great ValleyQuaternary alluvial gravel, sand, silt, clay.Low838.6%
Southern Coast RangesMetamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited.Moderate915.6%

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

Fresno County beside the ground around it

Across California 0.1% of the land is rated high; none of Fresno County's is. Of the 8 counties that border it, 1 has more high-potential ground, Inyo County the most at 1.0%.

Share of land by USGS radon potential: Fresno County, the 8 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
Fresno CountyZone 238.6%61.4%None
Madera CountyZone 236.6%63.4%None
Kings CountyZone 374.8%25.2%None
Tulare CountyZone 227.2%72.8%None
Merced CountyZone 365.2%34.8%None
San Benito CountyZone 2None100%None
Mono CountyZone 2None100%None
Monterey CountyZone 2None100%None
Inyo CountyZone 2None99.0%1.0%
California58 counties, pooled by land areaVaries57.2%42.6%0.1%

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

Local help

Fresno County, Local resources

Radon testing and mitigation in Fresno County

What California's program says
Phone
1-800-745-7236
Email
Radonprogram@cdph.ca.gov
Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.

What it means

Fresno County, Questions

Questions about radon in Fresno County

Are radon levels high in Fresno County?

Over the 2008 to 2017 laboratory totals, 11.0% of the radon tests reported to CDC for Fresno County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.5 pCi/L. Of 33 California counties with 30 or more tests for the same period, 16 reported a higher share; pooled, the state comes to 10.3%.

Which counties border Fresno County?

Fresno County borders 8 counties: Madera County, Kings County, Tulare County, Merced County, San Benito County, Mono County, Monterey County and Inyo County.

Products

Fresno County, Products

Testing a home in Fresno County

In Fresno County, 11.0% of 100 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Fresno County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Fresno County homes, compared

Explore

Fresno County, Bordering counties

Counties bordering Fresno County

Calculated by Radon411

Fresno County, Cities and towns

Cities and towns in Fresno County

The Census Bureau estimates 1,035,456 residents in Fresno County for July 1, 2025, 25,893 more than in 2020 (+2.6%). That works out to 174 people per square mile of land. Fresno alone is home to 555,549 of them, 53.7% of the total. Together its 15 incorporated places hold 84.7% of those residents; the other 15.3% live outside any of them. Reported testing is thin here: 100 tests over 2008 to 2017, or 0.1 for every 1,000 residents (2025 estimate), where California as a whole comes to 0.2.

From Fresno to San Joaquin, CDC publishes no figure by town: each reads Fresno County's.

The 12 largest cities and towns in Fresno County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Fresno555,549+2.4%53.7%
Clovis129,347+7.1%12.5%
Sanger27,228+1.6%2.6%
Reedley26,982+7.0%2.6%
Selma24,702−0.3%2.4%
Kerman17,553+9.5%1.7%
Coalinga17,281−2.4%1.7%
Parlier14,622+0.3%1.4%
Kingsburg13,249+6.6%1.3%
Mendota12,778+1.5%1.2%
Orange Cove9,811+0.7%0.9%
Firebaugh8,774+7.8%0.8%
  • Fowler
  • Huron
  • San Joaquin

15 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).

Fresno County, Homes

Homes in Fresno County

Of Fresno County's 342,003 homes, 68% are detached houses, against 57% across California; 16% are in buildings of five or more homes. Half of its homes were built before 1981, close to California's 1976: 20% date from before 1960 and 25% from 2000 or later. 55% of occupied homes are lived in by their owner (California: 56%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Fresno County, California, 2019 to 2023
HomesFresno CountyCalifornia
Housing units342,00314,532,683
Detached houses68%57%
In buildings of 5 or more16%24%
Mobile homes4%4%
Built before 196020%27%
Built since 200025%18%
Middle year built19811976
Owner-occupied55%56%

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