Skip to content
RADON411

Locations and reports

Radon Levels in Placer County, California

EPA puts Placer County in Zone 2, its middle radon zone, and most reported tests there come back low, though 7.4% of 283 (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

    7.4%

    2.9 pts below CA

    Placer
    7.4%
    California
    10.3%

    283 tests, 2008 to 2017

  • Median result

    1.1pCi/L

    Below action level

    Placer
    1.1 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    283

    10th of 33 by tests

    Placer
    283
    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

    24 of 33

    Middle half

    Placer
    7.4%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for Placer County

Starts at Placer County's median, 1.1 pCi/L

1.1pCi/L

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

EPA’s reading of 1.1 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. Placer County's median reported result, 2008 to 2017.

Interpret this reading

The data

Placer County, At a glance

Placer County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Placer 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 92% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Placer County, 2008 to 2017, laboratory
Under 2 pCi/L: 78%2 to 4 pCi/L: 15%4 pCi/L and above: 7%

Of 283 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Placer County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L22178.1%
2 to 4 pCi/L4114.5%
4 pCi/L and above217.4%
What these figures count

These are the 283 tests reported to CDC for Placer 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

Placer County, Compared

Placer County radon figures, compared

Calculated by Radon411

Placer County reports fewer high tests than California overall. 7.4% of its 283 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 2.9 points below the 10.3% pooled from 56 California counties.

Ordered from highest share down, it comes 24th 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%; Placer County sits 28.3 points below it.

Next door, the shares run from 7.7% in Sacramento County to 40.6% in Carson City, NV. The reported tests do not follow EPA's Zone 2 label for Placer County (predicted average between 2 and 4 pCi/L): 7.4% of them reached 4 pCi/L, fewer than that label suggests.

Half the tests came in under 1.1 pCi/L and half over it; the single highest reached 23.7 pCi/L. The rest split 78.1% under 2 pCi/L and 14.5% from 2 to 4 (California: 76.8% and 12.9%).

CDC's ten-year totals for Placer County went from 241 tests (2005 to 2014) to 283 (2008 to 2017), the share going from 7.9% to 7.4%.

Placer County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Placer County
Placer County2837.4%1.1 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled+2.9 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+28.3 points
Amador Countyhighest in the state3627.8%2.3 pCi/L+20.4 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−6.6 points
Sutter County, CAborders it742.9%1.9 pCi/L+35.5 points
Carson City, NVborders it73140.6%3.3 pCi/L+33.2 points
Douglas County, NVborders it1,61737.0%3.1 pCi/L+29.6 points
El Dorado County, CAborders it27430.3%1.6 pCi/L+22.9 points
Nevada County, CAborders it26025.0%2.0 pCi/L+17.6 points
Washoe County, NVborders it5,04622.2%1.9 pCi/L+14.8 points
Sacramento County, CAborders it1947.7%0.9 pCi/L+0.3 points
Yuba County, CAborders it70.0%0.1 pCi/L−7.4 points
Where Placer County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultPlacer County testsPlacer County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L22178.1%76.8%39.6%+1.3 points
2 to 4 pCi/L4114.5%12.9%24.7%+1.6 points
4 pCi/L and above217.4%10.3%35.7%−2.9 points
Placer 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
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
Sacramento County23 of 331947.7%0.9 pCi/L
Placer County24 of 332837.4%1.1 pCi/L
Alameda County25 of 334786.7%0.7 pCi/L
Marin County26 of 33956.3%0.8 pCi/L
San Bernardino County27 of 331784.5%0.7 pCi/L
Orange County28 of 334313.9%0.7 pCi/L
San Francisco County29 of 332462.8%0.5 pCi/L
Placer County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20172837.4%1.1 pCi/L23.7 pCi/L10.3%−0.5 points
2007 to 20162777.9%1.1 pCi/L23.7 pCi/L10.6%−0.3 points
2006 to 20152568.2%1.2 pCi/L23.7 pCi/L10.6%+0.3 points
2005 to 20142417.9%1.1 pCi/L23.7 pCi/L10.0%First on file

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

Placer County, Geology

The ground under Placer County

Predicted

Most of the ground under Placer County is one class on USGS's geologic map: 92.3% of its land is moderate radon potential, with 7.7% low. The map puts 92.3% of Placer County in the area it calls Sierra Nevada and 7.7% in Great Valley. 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 Placer 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.Moderate992.3%
Great ValleyQuaternary alluvial gravel, sand, silt, clay.Low87.7%

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

Placer County beside the ground around it

Across California 0.1% of the land is rated high; none of Placer County's is. Of the 8 counties that border it, 4 have more moderate-potential ground, El Dorado County the most at 100%.

Share of land by USGS radon potential: Placer County, the 8 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
Placer CountyZone 27.7%92.3%None
El Dorado CountyZone 2None100%None
Nevada CountyZone 2None100%None
Yuba CountyZone 231.1%68.9%None
Sacramento CountyZone 378.0%20.3%None
Sutter CountyZone 3100%NoneNone
Carson City, NVZone 1None100%None
Douglas County, NVZone 1None100%None
Washoe County, NVZone 242.1%57.9%None
California58 counties, pooled by land areaVaries57.2%42.6%0.1%

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

Local help

Placer County, Local resources

Radon testing and mitigation in Placer 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

Placer County, Questions

Questions about radon in Placer County

Are radon levels high in Placer County?

Over the 2008 to 2017 laboratory totals, 7.4% of the radon tests reported to CDC for Placer County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.1 pCi/L. Of 33 California counties with 30 or more tests for the same period, 23 reported a higher share; pooled, the state comes to 10.3%.

Which counties border Placer County?

Placer County borders 8 counties: El Dorado County, CA, Nevada County, CA, Yuba County, CA, Sacramento County, CA, Sutter County, CA, Carson City, NV, Douglas County, NV and Washoe County, NV.

Products

Placer County, Products

Testing a home in Placer County

In Placer County, 7.4% of 283 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 Placer County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Placer County homes, compared

Explore

Placer County, Bordering counties

Counties bordering Placer County

Calculated by Radon411

Placer County, Cities and towns

Cities and towns in Placer County

Placer County is growing: the Census Bureau puts it at 442,081 residents on July 1, 2025, up 8.9% from 405,971 in 2020. That works out to 314 people per square mile of land. Its largest town, Roseville, has 167,302 residents, 37.8% of the total. Together its 6 incorporated places hold 73.4% of those residents; the other 26.6% live outside any of them. Testing is reported here more often than across the state: CDC's 283 reported tests for 2008 to 2017 come to 0.6 for every 1,000 residents (2025 estimate), against 0.2 for California.

From Roseville to Colfax, CDC publishes no figure by town: each reads Placer County's.

The cities and towns in Placer County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Roseville167,302+12.6%37.8%
Rocklin76,821+7.0%17.4%
Lincoln57,367+14.8%13.0%
Auburn13,847+0.5%3.1%
Loomis7,004+2.6%1.6%
Colfax2,043+3.7%0.5%

6 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).

Placer County, Homes

Homes in Placer County

Placer County is a place of houses on their own lots: 78% of its 176,233 homes are detached single-family houses, against 57% across California. Much of Placer County is recent building: 38% of its homes have gone up since 2000 and the middle year built is 1994, against 1976 for California. 74% 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 Placer County, California, 2019 to 2023
HomesPlacer CountyCalifornia
Housing units176,23314,532,683
Detached houses78%57%
In buildings of 5 or more11%24%
Mobile homes3%4%
Built before 19609%27%
Built since 200038%18%
Middle year built19941976
Owner-occupied74%56%

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