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Radon Levels in Johnson County, Wyoming

EPA puts Johnson County in Zone 1, its highest radon zone, and 34.8% of its 135 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

    34.8%

    9.5 pts below WY

    Johnson
    34.8%
    Wyoming
    44.3%

    135 tests, 2008 to 2017

  • Median result

    3.1pCi/L

    Below action level

    Johnson
    3.1 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    135

    13th of 22 by tests

    Johnson
    135
    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

    18 of 22

    Lowest quarter

    Johnson
    34.8%
    Sheridan
    69.5%

    By share, of 22 with 30+ tests

Read a result for Johnson County

Starts at Johnson County's median, 3.1 pCi/L

3.1pCi/L

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

EPA’s reading of 3.1 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. Johnson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Johnson County, At a glance

Johnson County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Johnson 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 86% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Johnson County, 2008 to 2017, laboratory
Under 2 pCi/L: 25%2 to 4 pCi/L: 40%4 pCi/L and above: 35%

Of 135 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Johnson County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L3425.2%
2 to 4 pCi/L5440.0%
4 pCi/L and above4734.8%
What these figures count

These are the 135 tests reported to CDC for Johnson 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

Johnson County, Compared

Johnson County radon figures, compared

Calculated by Radon411

In Johnson County, about 3 in 10 reported tests over the 2008 to 2017 laboratory totals (47 of 135) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 0.9 points lower. Across 23 Wyoming counties pooled together, 44.3% of tests reached that level, so Johnson County runs 9.5 points below its state.

Of 6 neighbours with a figure, all 6 reported a larger share at or above 4 pCi/L; the spread is 38.5% (Washakie County) to 69.5% (Sheridan County). By share, Johnson County is 18th of 22 Wyoming counties with 30 or more tests for the same period.

Half the tests came in under 3.1 pCi/L and half over it; the single highest reached 45.8 pCi/L. Below the action level, 34 tests (25.2%) came in under 2 pCi/L, against 25.5% statewide, and 54 tests (40.0%) fell between 2 and 4, against 30.2% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 34.8% share point the same way here. USGS geology rates 86% of the county's land high radon potential.

CDC's ten-year totals for Johnson County went from 135 tests (2005 to 2014) to 135 (2008 to 2017), the share going from 35.6% to 34.8%.

Johnson County against Wyoming, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Johnson County
Johnson County13534.8%3.1 pCi/LThis county
Wyoming, pooled23 counties, pooled7,63844.3%Not pooled+9.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+0.9 points
Lincoln Countyhighest in the state14268.3%7.8 pCi/L+33.5 points
Uinta Countylowest in the state19924.6%2.2 pCi/L−10.2 points
Sheridan County, WYborders it84669.5%5.8 pCi/L+34.7 points
Converse County, WYborders it13062.3%4.8 pCi/L+27.5 points
Natrona County, WYborders it1,05455.7%4.3 pCi/L+20.9 points
Campbell County, WYborders it27143.9%3.5 pCi/L+9.1 points
Big Horn County, WYborders it9942.4%3.5 pCi/L+7.6 points
Washakie County, WYborders it13038.5%3.2 pCi/L+3.7 points
Where Johnson County's reported results fell, 2008 to 2017, laboratory, beside Wyoming and the United States
ResultJohnson County testsJohnson County shareWyoming shareU.S. shareAgainst Wyoming
Under 2 pCi/L3425.2%25.5%39.6%−0.3 points
2 to 4 pCi/L5440.0%30.2%24.7%+9.8 points
4 pCi/L and above4734.8%44.3%35.7%−9.5 points
Johnson 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
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
Platte County20 of 2213226.5%2.4 pCi/L
Laramie County21 of 221,83425.5%2.5 pCi/L
Uinta County22 of 2219924.6%2.2 pCi/L
Johnson County ten-year laboratory totals, against Wyoming's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestWyoming, pooledChange from the row before
2008 to 201713534.8%3.1 pCi/L45.8 pCi/L44.3%−1.1 points
2007 to 201613135.9%3.1 pCi/L45.8 pCi/L44.6%−2.0 points
2006 to 201512437.9%3.1 pCi/L45.8 pCi/L45.3%+2.3 points
2005 to 201413535.6%3.2 pCi/L20.8 pCi/L45.5%First on file

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

Johnson County, Geology

The ground under Johnson County

Predicted

Most of the ground under Johnson County is one class on USGS's geologic map: 85.6% of its land is high radon potential, with 14.4% moderate. The map puts 53.7% of Johnson County in the area it calls Powder River Basin and 31.9% in Big Horn Mountains, with one smaller area beside them. USGS gives both a radon index of 12, in the high band (12 to 17).

USGS's geologic areas under Johnson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Powder River BasinCretaceous and Tertiary uranium-bearing marginal-marine and fluvial sandstones.High1253.7%
Big Horn MountainsPrecambrian granitic and metamorphic rocks locally overlain by marine clastic and carbonate sedimentary rocks.High1231.9%
Casper Arch AreaUpper Cretaceous marine sedimentary rocks.Moderate1114.4%

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

Johnson County beside the ground around it

Johnson County has more high-potential ground than Wyoming as a whole: 85.6% of its land against 72.4%. Of the 6 counties that border it, 5 have more high-potential ground, Big Horn County the most at 100%.

Share of land by USGS radon potential: Johnson County, the 6 counties bordering it and Wyoming
AreaEPA zoneLow potentialModerate potentialHigh potential
Johnson CountyZone 1None14.4%85.6%
Washakie CountyZone 1NoneNone100%
Campbell CountyZone 1None2.4%97.6%
Sheridan CountyZone 1None1.9%98.1%
Natrona CountyZone 1None39.4%60.6%
Converse CountyZone 1None12.5%87.5%
Big Horn CountyZone 1NoneNone100%
Wyoming23 counties, pooled by land areaVariesNone27.6%72.4%

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

Local help

Johnson County, Local resources

Radon testing and mitigation in Johnson County

What it means

Johnson County, Questions

Questions about radon in Johnson County

Are radon levels high in Johnson County?

Over the 2008 to 2017 laboratory totals, 34.8% of the radon tests reported to CDC for Johnson County, Wyoming were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.1 pCi/L. Of 22 Wyoming counties with 30 or more tests for the same period, 17 reported a higher share; pooled, the state comes to 44.3%.

Which counties border Johnson County?

Johnson County borders 6 counties: Washakie County, Campbell County, Sheridan County, Natrona County, Converse County and Big Horn County.

Products

Johnson County, Products

Testing a home in Johnson County

In Johnson County, 34.8% of 135 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 Johnson 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

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

Explore

Johnson County, Bordering counties

Counties bordering Johnson County

Calculated by Radon411

Johnson County, Cities and towns

Cities and towns in Johnson County

Johnson County is growing: the Census Bureau puts it at 8,908 residents on July 1, 2025, up 5.2% from 8,469 in 2020. Spread over its land, that is 2.1 people to the square mile. Buffalo alone is home to 4,733 of them, 53.1% of the total. Together its 2 incorporated places hold 56.3% of those residents; the other 43.7% live outside any of them. CDC's 135 reported tests for 2008 to 2017 work out to 15.2 per 1,000 residents (2025 estimate), close to Wyoming's 13.0.

From Buffalo to Kaycee, CDC publishes no figure by town: each reads Johnson County's.

The cities and towns in Johnson County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Buffalo4,733+6.6%53.1%
Kaycee285+14.9%3.2%

2 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).

Johnson County, Homes

Homes in Johnson County

Johnson County is a place of houses on their own lots: 78% of its 4,635 homes are detached single-family houses, against 68% across Wyoming. Half of its homes were built before 1985, close to Wyoming's 1980: 28% date from before 1960 and 29% from 2000 or later. Owners live in 80% of the occupied homes (Wyoming: 72%), so for most households a test and a fix are their own to order.

Homes in Johnson County, Wyoming, 2019 to 2023
HomesJohnson CountyWyoming
Housing units4,635275,131
Detached houses78%68%
In buildings of 5 or more5%9%
Mobile homes11%12%
Built before 196028%24%
Built since 200029%24%
Middle year built19851980
Owner-occupied80%72%

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