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Radon Levels in Natrona County, Wyoming

EPA puts Natrona County in Zone 1, its highest radon zone, and high results are common there: 55.7% of the 1,054 radon tests reported to CDC (2008 to 2017, laboratory totals) came back 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

    55.7%

    11.4 pts above WY

    Natrona
    55.7%
    Wyoming
    44.3%

    1,054 tests, 2008 to 2017

  • Median result

    4.3pCi/L

    Action level reached

    Natrona
    4.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,054

    2nd of 22 by tests

    Natrona
    1,054
    Laramie
    1,834

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Wyoming

    7 of 22

    Middle half

    Natrona
    55.7%
    Sheridan
    69.5%

    By share, of 22 with 30+ tests

Read a result for Natrona County

Starts at Natrona County's median, 4.3 pCi/L

4.3pCi/L

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

EPA’s reading of 4.3 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. Natrona County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Natrona County, At a glance

Natrona County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Natrona County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

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

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Natrona County, 2008 to 2017, laboratory
Under 2 pCi/L: 17%2 to 4 pCi/L: 27%4 pCi/L and above: 56%

Of 1,054 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Natrona County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L17917.0%
2 to 4 pCi/L28827.3%
4 pCi/L and above58755.7%
What these figures count

These are the 1,054 tests reported to CDC for Natrona 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

Natrona County, Compared

Natrona County radon figures, compared

Calculated by Radon411

More than half: 55.7% of the 1,054 radon tests reported to CDC for Natrona County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 7th of 22 Wyoming counties with 30 or more tests for the same period. That is 11.4 points above the 44.3% pooled from 23 Wyoming counties.

The median result, 4.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 48.3 pCi/L. The rest split 17.0% under 2 pCi/L and 27.3% from 2 to 4 (Wyoming: 25.5% and 30.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 55.7% share point the same way here.

1 of its 5 bordering counties with figures ran higher, led by Converse County at 62.3%; Johnson County reported 34.8%. Statewide for the same period, Sheridan County reported the highest share (69.5%) and Uinta County the lowest (24.6%).

CDC's ten-year totals for Natrona County went from 1,101 tests (2005 to 2014) to 1,054 (2008 to 2017), the share going from 56.9% to 55.7%.

Nationally, every county with a figure for the same period pools to 35.7%; Natrona County sits 20.0 points above it. CDC also counts 41 tests taken after mitigation in Natrona County for the same period: tests in homes where a fix was already in.

Natrona County against Wyoming, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Natrona County
Natrona County1,05455.7%4.3 pCi/LThis county
Wyoming, pooled23 counties, pooled7,63844.3%Not pooled−11.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−20.0 points
Sheridan Countyhighest in the state84669.5%5.8 pCi/L+13.8 points
Uinta Countylowest in the state19924.6%2.2 pCi/L−31.1 points
Converse County, WYborders it13062.3%4.8 pCi/L+6.6 points
Fremont County, WYborders it61855.7%4.7 pCi/LLevel
Carbon County, WYborders it8041.3%3.0 pCi/L−14.4 points
Washakie County, WYborders it13038.5%3.2 pCi/L−17.2 points
Johnson County, WYborders it13534.8%3.1 pCi/L−20.9 points
Where Natrona County's reported results fell, 2008 to 2017, laboratory, beside Wyoming and the United States
ResultNatrona County testsNatrona County shareWyoming shareU.S. shareAgainst Wyoming
Under 2 pCi/L17917.0%25.5%39.6%−8.5 points
2 to 4 pCi/L28827.3%30.2%24.7%−2.9 points
4 pCi/L and above58755.7%44.3%35.7%+11.4 points
Natrona County ranked among the 22 Wyoming counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Lincoln County2 of 2214268.3%7.8 pCi/L
Weston County3 of 223265.6%6.3 pCi/L
Converse County4 of 2213062.3%4.8 pCi/L
Crook County5 of 225158.8%5.1 pCi/L
Hot Springs County6 of 225955.9%4.2 pCi/L
Natrona County7 of 221,05455.7%4.3 pCi/L
Fremont County8 of 2261855.7%4.7 pCi/L
Sublette County9 of 226050.0%4.0 pCi/L
Sweetwater County10 of 2240949.6%3.9 pCi/L
Teton County11 of 2227844.6%3.4 pCi/L
Campbell County12 of 2227143.9%3.5 pCi/L
Natrona County ten-year laboratory totals, against Wyoming's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestWyoming, pooledChange from the row before
2008 to 20171,05455.7%4.3 pCi/L48.3 pCi/L44.3%−0.9 points
2007 to 20161,02556.6%4.4 pCi/L48.3 pCi/L44.6%+0.3 points
2006 to 20151,05156.3%4.4 pCi/L48.3 pCi/L45.3%−0.6 points
2005 to 20141,10156.9%4.5 pCi/L48.3 pCi/L45.5%First on file

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

Natrona County, Geology

The ground under Natrona County

Predicted

USGS's geologic map splits Natrona County: 60.6% of its land is high radon potential and 39.4% moderate. The map puts 39.4% of Natrona County in the area it calls Casper Arch Area and 29.8% in Wind River Basin, with 4 smaller areas beside them. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 12, in the high band (12 to 17).

USGS's geologic areas under Natrona County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Casper Arch AreaUpper Cretaceous marine sedimentary rocks.Moderate1139.4%
Wind River BasinCretaceous and Tertiary uranium-bearing marginal-marine and fluvial sandstones.High1229.8%
Wind River MountainsPrecambrian granite, glacial till in valleys.High1218.4%
Big Horn MountainsPrecambrian granitic and metamorphic rocks locally overlain by marine clastic and carbonate sedimentary rocks.High1210.8%
Laramie MountainsPrecambrian anorthosite, monzonite, gneissic granite, and granite.High121.0%
Powder River BasinCretaceous and Tertiary uranium-bearing marginal-marine and fluvial sandstones.High120.5%

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

Natrona County beside the ground around it

Wyoming as a whole has more high-potential ground than Natrona County: 72.4% of its land, against 60.6% here. Every one of the 5 counties that border it has more high-potential ground, Washakie County the most at 100%.

Share of land by USGS radon potential: Natrona County, the 5 counties bordering it and Wyoming
AreaEPA zoneLow potentialModerate potentialHigh potential
Natrona CountyZone 1None39.4%60.6%
Converse CountyZone 1None12.5%87.5%
Johnson CountyZone 1None14.4%85.6%
Washakie CountyZone 1NoneNone100%
Carbon CountyZone 1None29.2%70.8%
Fremont CountyZone 1None7.3%92.7%
Wyoming23 counties, pooled by land areaVariesNone27.6%72.4%

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

Local help

Natrona County, Local resources

Radon testing and mitigation in Natrona County

What it means

Natrona County, Questions

Questions about radon in Natrona County

Are radon levels high in Natrona County?

Over the 2008 to 2017 laboratory totals, 55.7% of the radon tests reported to CDC for Natrona County, Wyoming were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.3 pCi/L. Of 22 Wyoming counties with 30 or more tests for the same period, 6 reported a higher share; pooled, the state comes to 44.3%.

Which counties border Natrona County?

Natrona County borders 5 counties: Converse County, Johnson County, Washakie County, Carbon County and Fremont County.

Products

Natrona County, Products

Testing a home in Natrona County

In Natrona County, 55.7% of 1,054 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 44.3% pooled across Wyoming. In Zone 1 the year-round level in Natrona County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.

Test kits and monitors3

See every kit and monitor

Natrona County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Natrona County

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Natrona County, Bordering counties

Counties bordering Natrona County

Calculated by Radon411

Natrona County, Cities and towns

Cities and towns in Natrona County

Natrona County's population has barely moved since 2020: 80,526 residents on July 1, 2025 against 80,299 then, by the Census Bureau's estimates. That works out to 15 people per square mile of land. Casper alone is home to 58,771 of them, 73.0% of the total. Together its 6 incorporated places hold 86.6% of those residents; the other 13.4% live outside any of them. CDC's 1,054 reported tests for 2008 to 2017 work out to 13.1 per 1,000 residents (2025 estimate), close to Wyoming's 13.0.

From Casper to Edgerton, CDC publishes no figure by town: each reads Natrona County's.

The cities and towns in Natrona County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Casper58,771−0.9%73.0%
Mills4,634+9.6%5.8%
Bar Nunn3,012+0.5%3.7%
Evansville2,875+3.3%3.6%
Midwest292+1.7%0.4%
Edgerton158+2.6%0.2%

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).

Natrona County, Homes

Homes in Natrona County

Of Natrona County's 37,101 homes, 71% are detached houses, against 68% across Wyoming; 13% are in buildings of five or more homes. Half of its homes were built before 1977, close to Wyoming's 1980: 30% date from before 1960 and 25% from 2000 or later. 74% of occupied homes are lived in by their owner (Wyoming: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Natrona County, Wyoming, 2019 to 2023
HomesNatrona CountyWyoming
Housing units37,101275,131
Detached houses71%68%
In buildings of 5 or more13%9%
Mobile homes8%12%
Built before 196030%24%
Built since 200025%24%
Middle year built19771980
Owner-occupied74%72%

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