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Radon Levels in Big Horn County, Wyoming

EPA puts Big Horn County in Zone 1, its highest radon zone, and high results are common there: 42.4% of the 99 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

    42.4%

    1.9 pts below WY

    Big Horn
    42.4%
    Wyoming
    44.3%

    99 tests, 2008 to 2017

  • Median result

    3.5pCi/L

    Below action level

    Big Horn
    3.5 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    99

    17th of 22 by tests

    Big Horn
    99
    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

    14 of 22

    Middle half

    Big Horn
    42.4%
    Sheridan
    69.5%

    By share, of 22 with 30+ tests

Read a result for Big Horn County

Starts at Big Horn County's median, 3.5 pCi/L

3.5pCi/L

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

EPA’s reading of 3.5 pCi/L

Between 2 and 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Big Horn County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Big Horn County, At a glance

Big Horn County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Big Horn 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Big Horn County, 2008 to 2017, laboratory

Reported results by concentration band, Big Horn County, 2008 to 2017, laboratory
Under 2 pCi/L: 18%2 to 4 pCi/L: 40%4 pCi/L and above: 42%

Of 99 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Big Horn County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1818.2%
2 to 4 pCi/L3939.4%
4 pCi/L and above4242.4%
What these figures count

These are the 99 tests reported to CDC for Big Horn 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

Big Horn County, Compared

Big Horn County radon figures, compared

Calculated by Radon411

In Big Horn County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (42 of 99) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 6.7 points higher. Across 23 Wyoming counties pooled together, 44.3% of tests reached that level, so Big Horn County runs 1.9 points below its state.

Of 5 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 2 a smaller one; the spread is 34.8% (Johnson County) to 69.5% (Sheridan County). By share, Big Horn County is 14th of 22 Wyoming counties with 30 or more tests for the same period.

Half the tests came in under 3.5 pCi/L and half over it; the single highest reached 18.8 pCi/L. Below the action level, 18 tests (18.2%) came in under 2 pCi/L, against 25.5% statewide, and 39 tests (39.4%) fell between 2 and 4, against 30.2% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 42.4% share point the same way here. USGS geology rates 100% of the county's land high radon potential.

CDC's ten-year totals for Big Horn County went from 88 tests (2005 to 2014) to 99 (2008 to 2017), the share going from 45.5% to 42.4%.

Big Horn County against Wyoming, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Big Horn County
Big Horn County9942.4%3.5 pCi/LThis county
Wyoming, pooled23 counties, pooled7,63844.3%Not pooled+1.9 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−6.7 points
Lincoln Countyhighest in the state14268.3%7.8 pCi/L+25.9 points
Uinta Countylowest in the state19924.6%2.2 pCi/L−17.8 points
Sheridan County, WYborders it84669.5%5.8 pCi/L+27.1 points
Carbon County, MTborders it4652.2%4.2 pCi/L+9.8 points
Park County, WYborders it50542.8%3.4 pCi/L+0.4 points
Washakie County, WYborders it13038.5%3.2 pCi/L−3.9 points
Johnson County, WYborders it13534.8%3.1 pCi/L−7.6 points
Big Horn County, MTborders it2128.6%2.0 pCi/L−13.8 points
Where Big Horn County's reported results fell, 2008 to 2017, laboratory, beside Wyoming and the United States
ResultBig Horn County testsBig Horn County shareWyoming shareU.S. shareAgainst Wyoming
Under 2 pCi/L1818.2%25.5%39.6%−7.3 points
2 to 4 pCi/L3939.4%30.2%24.7%+9.2 points
4 pCi/L and above4242.4%44.3%35.7%−1.9 points
Big Horn 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
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
Park County13 of 2250542.8%3.4 pCi/L
Big Horn County14 of 229942.4%3.5 pCi/L
Goshen County15 of 2216841.7%3.3 pCi/L
Carbon County16 of 228041.3%3.0 pCi/L
Washakie County17 of 2213038.5%3.2 pCi/L
Johnson County18 of 2213534.8%3.1 pCi/L
Albany County19 of 2239427.9%2.7 pCi/L
Big Horn County ten-year laboratory totals, against Wyoming's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestWyoming, pooledChange from the row before
2008 to 20179942.4%3.5 pCi/L18.8 pCi/L44.3%−2.7 points
2007 to 20169145.1%3.6 pCi/L18.8 pCi/L44.6%+0.9 points
2006 to 20158644.2%3.5 pCi/L17.8 pCi/L45.3%−1.3 points
2005 to 20148845.5%3.5 pCi/L17.8 pCi/L45.5%First on file

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

Big Horn County, Geology

The ground under Big Horn County

Predicted

USGS's geologic map puts all of Big Horn County's mapped land in one class: high radon potential. The map puts 65.6% of Big Horn County in the area it calls Big Horn Basin and 34.4% in Big Horn Mountains. USGS gives both a radon index of 12, in the high band (12 to 17).

USGS's geologic areas under Big Horn County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Big Horn BasinCretaceous and Tertiary uranium-bearing marginal-marine and fluvial sandstones.High1265.6%
Big Horn MountainsPrecambrian granitic and metamorphic rocks locally overlain by marine clastic and carbonate sedimentary rocks.High1234.4%

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

Big Horn County beside the ground around it

Big Horn County has more high-potential ground than Wyoming as a whole: 100% of its land against 72.4%. Of the 6 counties that border it, none has as large a share of high-potential ground; Washakie County comes nearest at 100%.

Share of land by USGS radon potential: Big Horn County, the 6 counties bordering it and Wyoming
AreaEPA zoneLow potentialModerate potentialHigh potential
Big Horn CountyZone 1NoneNone100%
Washakie CountyZone 1NoneNone100%
Sheridan CountyZone 1None1.9%98.1%
Park CountyZone 1None51.9%48.1%
Big Horn County, MTZone 1None49.8%50.2%
Carbon County, MTZone 1None82.0%18.0%
Johnson CountyZone 1None14.4%85.6%
Wyoming23 counties, pooled by land areaVariesNone27.6%72.4%

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

Local help

Big Horn County, Local resources

Radon testing and mitigation in Big Horn County

What it means

Big Horn County, Questions

Questions about radon in Big Horn County

Are radon levels high in Big Horn County?

Over the 2008 to 2017 laboratory totals, 42.4% of the radon tests reported to CDC for Big Horn County, Wyoming were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.5 pCi/L. Of 22 Wyoming counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 44.3%.

Which counties border Big Horn County?

Big Horn County borders 6 counties: Washakie County, WY, Sheridan County, WY, Park County, WY, Big Horn County, MT, Carbon County, MT and Johnson County, WY.

Products

Big Horn County, Products

Testing a home in Big Horn County

In Big Horn County, 42.4% of 99 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 Big Horn 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

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

Explore

Big Horn County, Bordering counties

Counties bordering Big Horn County

Calculated by Radon411

Big Horn County, Cities and towns

Cities and towns in Big Horn County

The Census Bureau estimates 12,024 residents in Big Horn County for July 1, 2025, 544 more than in 2020 (+4.7%). Spread over its land, that is 3.8 people to the square mile. No town dominates: Lovell, the largest, has 2,351 residents, 19.6% of the total. Reported testing is thin here: 99 tests over 2008 to 2017, or 8.2 for every 1,000 residents (2025 estimate), where Wyoming as a whole comes to 13.0.

From Lovell to Manderson, CDC publishes no figure by town: each reads Big Horn County's.

The cities and towns in Big Horn County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Lovell2,351+5.0%19.6%
Greybull1,700+3.5%14.1%
Basin1,334+4.0%11.1%
Cowley855+11.9%7.1%
Byron572+3.1%4.8%
Burlington393+24.4%3.3%
Deaver170+11.1%1.4%
Frannieextends beyond Big Horn County144+5.1%Counted whole
Manderson90+2.3%0.7%

9 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). A place that extends beyond Big Horn County is counted whole, so it has no share.

Big Horn County, Homes

Homes in Big Horn County

Big Horn County is a place of houses on their own lots: 79% of its 5,370 homes are detached single-family houses, against 68% across Wyoming. The homes are older than Wyoming's as a whole: half were built before 1967 (1980 for Wyoming), and 44% date from before 1960. Owners live in 77% of the occupied homes (Wyoming: 72%), so for most households a test and a fix are their own to order.

Homes in Big Horn County, Wyoming, 2019 to 2023
HomesBig Horn CountyWyoming
Housing units5,370275,131
Detached houses79%68%
In buildings of 5 or more3%9%
Mobile homes15%12%
Built before 196044%24%
Built since 200014%24%
Middle year built19671980
Owner-occupied77%72%

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