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Radon Levels in Custer County, South Dakota

EPA puts Custer County in Zone 2, its middle radon zone, and high results are common there: 65.7% of the 108 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

    65.7%

    7.2 pts above SD

    Custer
    65.7%
    SD
    58.5%

    108 tests, 2008 to 2017

  • Median result

    6.2pCi/L

    Action level reached

    Custer
    6.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    108

    9th of 23 by tests

    Custer
    108
    Minnehaha
    1,920

    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 SD

    10 of 23

    Middle half

    Custer
    65.7%
    Lake
    76.0%

    By share, of 23 with 30+ tests

Read a result for Custer County

Starts at Custer County's median, 6.2 pCi/L

6.2pCi/L

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

EPA’s reading of 6.2 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. Custer County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Custer County, At a glance

Custer County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Custer 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 88% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Custer County, 2008 to 2017, laboratory
Under 2 pCi/L: 17%2 to 4 pCi/L: 17%4 pCi/L and above: 66%

Of 108 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Custer County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1816.7%
2 to 4 pCi/L1917.6%
4 pCi/L and above7165.7%
What these figures count

These are the 108 tests reported to CDC for Custer 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

Custer County, Compared

Custer County radon figures, compared

Calculated by Radon411

More than half: 65.7% of the 108 radon tests reported to CDC for Custer County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 10th of 23 South Dakota counties with 30 or more tests for the same period. That is 7.2 points above the 58.5% pooled from 62 South Dakota counties.

The median result, 6.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 979.5 pCi/L. The rest split 16.7% under 2 pCi/L and 17.6% from 2 to 4 (South Dakota: 23.6% and 17.9%). The reported tests do not follow EPA's Zone 2 label for Custer County (predicted average between 2 and 4 pCi/L): 65.7% of them reached 4 pCi/L, fewer than that label suggests.

No bordering county with a figure for the same period reported a higher share; the closest is Weston County, WY at 65.6%, the lowest Pennington County at 53.6%. Statewide for the same period, Lake County reported the highest share (76.0%) and Davison County the lowest (48.8%).

CDC's ten-year totals for Custer County went from 78 tests (2005 to 2014) to 108 (2008 to 2017), the share going from 66.7% to 65.7%.

Nationally, every county with a figure for the same period pools to 35.7%; Custer County sits 30.0 points above it.

Custer County against South Dakota, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Custer County
Custer County10865.7%6.2 pCi/LThis county
South Dakota, pooled62 counties, pooled6,27558.5%Not pooled−7.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−30.0 points
Lake Countyhighest in the state5076.0%8.5 pCi/L+10.3 points
Davison Countylowest in the state8448.8%3.8 pCi/L−16.9 points
Weston County, WYborders it3265.6%6.3 pCi/L−0.1 points
Fall River County, SDborders it2462.5%5.8 pCi/L−3.2 points
Pennington County, SDborders it1,02953.6%4.3 pCi/L−12.1 points
Niobrara County, WYborders it1225.0%3.5 pCi/L−40.7 points
Where Custer County's reported results fell, 2008 to 2017, laboratory, beside South Dakota and the United States
ResultCuster County testsCuster County shareSouth Dakota shareU.S. shareAgainst South Dakota
Under 2 pCi/L1816.7%23.6%39.6%−6.9 points
2 to 4 pCi/L1917.6%17.9%24.7%−0.3 points
4 pCi/L and above7165.7%58.5%35.7%+7.2 points
Custer County ranked among the 23 South Dakota counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Hughes County5 of 237170.4%5.7 pCi/L
Brookings County6 of 2335668.5%6.6 pCi/L
Kingsbury County7 of 234468.2%7.4 pCi/L
Brule County8 of 233767.6%6.4 pCi/L
Hutchinson County9 of 233966.7%5.8 pCi/L
Custer County10 of 2310865.7%6.2 pCi/L
Codington County11 of 237764.9%5.8 pCi/L
Beadle County12 of 235459.3%4.8 pCi/L
Turner County13 of 235858.6%4.8 pCi/L
Minnehaha County14 of 231,92058.5%4.8 pCi/L
Lawrence County15 of 2316056.9%5.3 pCi/L
Custer County ten-year laboratory totals, against South Dakota's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestSouth Dakota, pooledChange from the row before
2008 to 201710865.7%6.2 pCi/L979.5 pCi/L58.5%−3.2 points
2007 to 20169068.9%8.0 pCi/L979.5 pCi/L57.4%+0.6 points
2006 to 20158268.3%7.2 pCi/L979.5 pCi/L58.8%+1.6 points
2005 to 20147866.7%6.5 pCi/L979.5 pCi/L59.6%First on file

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

Custer County, Geology

The ground under Custer County

Predicted

Most of the ground under Custer County is one class on USGS's geologic map: 88.4% of its land is moderate radon potential, with 11.6% high. The map puts 59.7% of Custer County in the area it calls Black Hills and 28.7% in Pierre Hills, with one smaller area beside them. USGS gives the first a radon index of 11 and the second 10, both in the moderate band (9 to 11).

USGS's geologic areas under Custer County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Black HillsLate Paleozoic sedimentary or Precambrian intrusive igneous rocks.Moderate1159.7%
Pierre HillsPierre Shale and Fox Hills sandstone.Moderate1028.7%
Black HillsSandstones and shales of Cretaceous age that surround the Black Hills.High1411.6%

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

Custer County beside the ground around it

South Dakota as a whole has more high-potential ground than Custer County: 56.7% of its land, against 11.6% here. Of the 5 counties that border it, 3 have more high-potential ground, Weston County, WY the most at 45.1%.

Share of land by USGS radon potential: Custer County, the 5 counties bordering it and South Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Custer CountyZone 2None88.4%11.6%
Pennington CountyZone 2None96.0%4.0%
Fall River CountyZone 2None63.4%36.6%
Oglala Lakota CountyZone 21.9%98.1%None
Weston County, WYZone 2None54.9%45.1%
Niobrara County, WYZone 1None69.5%30.5%
South Dakota66 counties, pooled by land areaVaries1.0%42.3%56.7%

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

Local help

Custer County, Local resources

Radon testing and mitigation in Custer County

What South Dakota's program says
Phone
1-800-438-3367

What it means

Custer County, Questions

Questions about radon in Custer County

Are radon levels high in Custer County?

Over the 2008 to 2017 laboratory totals, 65.7% of the radon tests reported to CDC for Custer County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.2 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, 9 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Custer County?

Custer County borders 5 counties: Pennington County, SD, Fall River County, SD, Oglala Lakota County, SD, Weston County, WY and Niobrara County, WY.

Products

Custer County, Products

Testing a home in Custer County

In Custer County, 65.7% of 108 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across South Dakota. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Custer County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Custer County homes, compared

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Custer County, Bordering counties

Counties bordering Custer County

Calculated by Radon411

Custer County, Cities and towns

Cities and towns in Custer County

Custer County is growing: the Census Bureau puts it at 9,431 residents on July 1, 2025, up 13.2% from 8,333 in 2020. Spread over its land, that is 6.1 people to the square mile. No town dominates: Custer, the largest, has 1,803 residents, 19.1% of the total. Together its 5 incorporated places hold 26.5% of those residents; the other 73.5% live outside any of them. Testing is reported here more often than across the state: CDC's 108 reported tests for 2008 to 2017 come to 11.5 for every 1,000 residents (2025 estimate), against 6.7 for South Dakota.

From Custer to Fairburn, CDC publishes no figure by town: each reads Custer County's.

The cities and towns in Custer County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Custer1,803−6.8%19.1%
Hermosa370−3.1%3.9%
Buffalo Gap155+21.1%1.6%
Pringle104−5.5%1.1%
Fairburn69+21.1%0.7%

5 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).

Custer County, Homes

Homes in Custer County

Of Custer County's 5,126 homes, 73% are detached houses, against 67% across South Dakota; 18% are mobile homes. Much of Custer County is recent building: 41% of its homes have gone up since 2000 and the middle year built is 1990, against 1979 for South Dakota. Owners live in 86% of the occupied homes (South Dakota: 69%), so for most households a test and a fix are their own to order.

Homes in Custer County, South Dakota, 2019 to 2023
HomesCuster CountySouth Dakota
Housing units5,126402,364
Detached houses73%67%
In buildings of 5 or more5%16%
Mobile homes18%8%
Built before 196022%29%
Built since 200041%28%
Middle year built19901979
Owner-occupied86%69%

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