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Radon Levels in Maricopa County, Arizona

EPA puts Maricopa County in Zone 2, its middle radon zone, and 17.4% of its 2,393 reported radon tests (2008 to 2017, laboratory totals) were at or above 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

    17.4%

    0.6 pts above AZ

    Maricopa
    17.4%
    Arizona
    16.8%

    2,393 tests, 2008 to 2017

  • Median result

    1.6pCi/L

    Below action level

    Maricopa
    1.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    2,393

    Most tested in Arizona

    Maricopa
    2,393

    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 Arizona

    2 of 6

    Top quarter

    Maricopa
    17.4%
    Coconino
    30.0%

    By share, of 6 with 30+ tests

Read a result for Maricopa County

Starts at Maricopa County's median, 1.6 pCi/L

1.6pCi/L

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

EPA’s reading of 1.6 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. Maricopa County's median reported result, 2008 to 2017.

Interpret this reading

The data

Maricopa County, At a glance

Maricopa County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Maricopa 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: Low across 84% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Maricopa County, 2008 to 2017, laboratory
Under 2 pCi/L: 59%2 to 4 pCi/L: 24%4 pCi/L and above: 17%

Of 2,393 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Maricopa County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1,39958.5%
2 to 4 pCi/L57824.2%
4 pCi/L and above41617.4%
What these figures count

These are the 2,393 tests reported to CDC for Maricopa 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

Maricopa County, Compared

Maricopa County radon figures, compared

Calculated by Radon411

Maricopa County's 2,393 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.6 pCi/L and a maximum of 61.4 pCi/L, and 17.4% reached 4 pCi/L. Arizona as a whole (13 Arizona counties, pooled) comes to 16.8%: 0.6 points lower than here.

Among its state's counties it ranks 2nd of 6 Arizona counties with 30 or more tests for the same period. Statewide for the same period, Coconino County reported the highest share (30.0%) and Mohave County the lowest (4.1%).

Below the action level, 1,399 tests (58.5%) came in under 2 pCi/L, against 60.1% statewide, and 578 tests (24.2%) fell between 2 and 4, against 23.2% statewide. CDC's ten-year totals for Maricopa County went from 2,101 tests (2005 to 2014) to 2,393 (2008 to 2017), the share going from 17.9% to 17.4%.

EPA's 1993 zone map puts Maricopa County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 84% of the county's land low radon potential.

Next door, the shares run from 6.8% in Pima County to 16.2% in Yavapai County, with Yavapai County, Pinal County and Pima County below Maricopa County.

CDC also counts 16 tests taken after mitigation in Maricopa County for the same period: tests in homes where a fix was already in.

Maricopa County against Arizona, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Maricopa County
Maricopa County2,39317.4%1.6 pCi/LThis county
Arizona, pooled13 counties, pooled3,58916.8%Not pooled−0.6 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+18.3 points
Coconino Countyhighest in the state27330.0%2.3 pCi/L+12.6 points
Mohave Countylowest in the state494.1%0.2 pCi/L−13.3 points
Gila County, AZborders it1764.7%5.7 pCi/L+47.3 points
Yavapai County, AZborders it26516.2%1.6 pCi/L−1.2 points
Pinal County, AZborders it1018.9%0.9 pCi/L−8.5 points
Pima County, AZborders it4106.8%1.1 pCi/L−10.6 points
Yuma County, AZborders it180.0%0.6 pCi/L−17.4 points
Where Maricopa County's reported results fell, 2008 to 2017, laboratory, beside Arizona and the United States
ResultMaricopa County testsMaricopa County shareArizona shareU.S. shareAgainst Arizona
Under 2 pCi/L1,39958.5%60.1%39.6%−1.6 points
2 to 4 pCi/L57824.2%23.2%24.7%+1.0 points
4 pCi/L and above41617.4%16.8%35.7%+0.6 points
Maricopa County ranked among the 6 Arizona counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Coconino County1 of 627330.0%2.3 pCi/L
Maricopa County2 of 62,39317.4%1.6 pCi/L
Yavapai County3 of 626516.2%1.6 pCi/L
Pinal County4 of 61018.9%0.9 pCi/L
Pima County5 of 64106.8%1.1 pCi/L
Mohave County6 of 6494.1%0.2 pCi/L
Maricopa County ten-year laboratory totals, against Arizona's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestArizona, pooledChange from the row before
2008 to 20172,39317.4%1.6 pCi/L61.4 pCi/L16.8%+0.2 points
2007 to 20162,34417.2%1.6 pCi/L61.4 pCi/L16.5%−1.0 points
2006 to 20152,19118.2%1.6 pCi/L61.4 pCi/L17.6%+0.3 points
2005 to 20142,10117.9%1.6 pCi/L61.4 pCi/L17.4%First on file

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

Maricopa County, Geology

The ground under Maricopa County

Predicted

Most of the ground under Maricopa County is one class on USGS's geologic map: 84.1% of its land is low radon potential, with 15.9% moderate. The map puts 84.1% of Maricopa County in the area it calls Basin and Range/Sonoran Desert and 15.9% in Transition Zone. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Maricopa County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Basin and Range/Sonoran DesertQuaternary to Tertiary sediments, with uranium-bearing Tertiary volcanic rocks, highly variable volcanic, metamorphic, and sedimentary rocks, and eolian depositsLow884.1%
Transition ZonePrecambrian igneous, metamorphic and sedimentary rocks and Tertiary volcanic rocks.Moderate1015.9%

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

Maricopa County beside the ground around it

Across Arizona 0.1% of the land is rated high; none of Maricopa County's is. Of the 6 counties that border it, 2 have more moderate-potential ground, Gila County the most at 100%.

Share of land by USGS radon potential: Maricopa County, the 6 counties bordering it and Arizona
AreaEPA zoneLow potentialModerate potentialHigh potential
Maricopa CountyZone 284.1%15.9%None
La Paz CountyZone 2100%NoneNone
Yuma CountyZone 299.9%NoneNone
Pinal CountyZone 284.9%15.1%None
Yavapai CountyZone 29.6%90.4%None
Pima CountyZone 2100%NoneNone
Gila CountyZone 2None100%None
Arizona15 counties, pooled by land areaVaries42.8%57.1%0.1%

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

Local help

Maricopa County, Local resources

Radon testing and mitigation in Maricopa County

What it means

Maricopa County, Questions

Questions about radon in Maricopa County

Are radon levels high in Maricopa County?

Over the 2008 to 2017 laboratory totals, 17.4% of the radon tests reported to CDC for Maricopa County, Arizona were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.6 pCi/L. Of 6 Arizona counties with 30 or more tests for the same period, 1 reported a higher share; pooled, the state comes to 16.8%.

Which counties border Maricopa County?

Maricopa County borders 6 counties: La Paz County, Yuma County, Pinal County, Yavapai County, Pima County and Gila County.

Products

Maricopa County, Products

Testing a home in Maricopa County

In Maricopa County, 17.4% of 2,393 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 16.8% pooled across Arizona. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Maricopa County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Maricopa County homes, compared

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Maricopa County, Bordering counties

Counties bordering Maricopa County

Calculated by Radon411

Maricopa County, Cities and towns

Cities and towns in Maricopa County

Maricopa County is growing: the Census Bureau puts it at 4,689,558 residents on July 1, 2025, up 5.5% from 4,445,025 in 2020. That works out to 510 people per square mile of land. Its largest town, Phoenix, has 1,665,481 residents, 35.5% of the total. CDC's 2,393 reported tests for 2008 to 2017 work out to 0.5 per 1,000 residents (2025 estimate), close to Arizona's 0.5.

From Phoenix to Gila Bend, CDC publishes no figure by town: each reads Maricopa County's.

The 12 largest cities and towns in Maricopa County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Phoenix1,665,481+3.3%35.5%
Mesa513,656+1.5%11.0%
Gilbert287,285+6.6%6.1%
Chandler278,748+0.5%5.9%
Glendale260,572+4.7%5.6%
Scottsdale243,006+0.5%5.2%
Peoriaextends beyond Maricopa County200,881+4.6%Counted whole
Tempe190,571+2.8%4.1%
Surprise175,304+21.4%3.7%
Buckeye125,445+34.3%2.7%
Goodyear125,359+28.2%2.7%
Avondale100,983+12.8%2.2%
  • Queen Creek (part)
  • Apache Junction (part)
  • El Mirage
  • Fountain Hills
  • Paradise Valley
  • Tolleson
  • Wickenburg (part)
  • Youngtown
  • Litchfield Park
  • Cave Creek
  • Guadalupe
  • Carefree
  • Gila Bend

25 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 Maricopa County is counted whole, so it has no share.

Maricopa County, Homes

Homes in Maricopa County

Of Maricopa County's 1,850,862 homes, 64% are detached houses, against 64% across Arizona; 20% are in buildings of five or more homes. Half of its homes were built before 1992, close to Arizona's 1992: 7% date from before 1960 and 35% from 2000 or later. 65% of occupied homes are lived in by their owner (Arizona: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Maricopa County, Arizona, 2019 to 2023
HomesMaricopa CountyArizona
Housing units1,850,8623,142,443
Detached houses64%64%
In buildings of 5 or more20%16%
Mobile homes5%10%
Built before 19607%8%
Built since 200035%35%
Middle year built19921992
Owner-occupied65%67%

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