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Radon Levels in Fall River County, South Dakota

EPA puts Fall River County in Zone 2, its middle radon zone, and only 24 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Highest bordering

    68.3%

    Custer County

    Custer
    68.3%
    Dawes
    56.9%

    2 of 5 neighbours have 30+ tests, 2006 to 2015

  • Nearest county

    68.3%

    Custer County, 30 miles

    Custer
    68.3%
    SD
    58.8%

    Share at 4+ pCi/L, 82 tests, 2006 to 2015

  • Ground above low

    100.0%

    1.0 pts above SD

    Fall River
    100.0%
    SD
    99.0%

    Share of land USGS rates moderate or high potential

  • Tests reported

    24

    Too few for a share

    Fall River
    24
    Needed
    30

    2008 to 2017, laboratory

  • 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

Read a result for Fall River County

Starts at EPA's action level

4.0pCi/L

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

EPA’s reading of 4.0 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.

Interpret this readingWhat a fix costs

The data

Fall River County, At a glance

Fall River County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Fall River 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 63% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Fall River County, 2008 to 2017, laboratory

CDC holds 24 reported tests for Fall River County over the 2008 to 2017 laboratory totals, with a median of 5.8 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Fall River County beside the counties around it is how this page reads it.

What these figures count

Only 24 tests were reported to CDC for Fall River County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor 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

Fall River County, Compared

Fall River County radon figures, compared

Calculated by Radon411

CDC's largest figure for Fall River County rests on 24 tests over the 2008 to 2017 laboratory totals, 15 of them at or above 4 pCi/L, so each test moves its share by 4.2 points and no rank or comparison is drawn from it. Results reached as high as 22.3 pCi/L, with a middle value of 5.8 pCi/L.

Of the counties bordering it, 2 have a figure over the 2006 to 2015 laboratory totals: Custer County reported the largest share at or above 4 pCi/L, 68.3%, and Dawes County, NE the smallest, 56.9%. Farther out, Pennington County (63 miles away) at 51.8%, Lawrence County (78 miles away) at 60.5% and Meade County (100 miles away) at 54.5% have figures too. Pooled across 63 South Dakota counties, 58.8% of reported tests reached that level; across every county in the country with a figure, 36.3%.

Statewide for the same period, Bon Homme County reported the highest share (79.5%) and Davison County the lowest (47.9%). EPA's 1993 map puts Fall River County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 63% of the county's land moderate radon potential.

South Dakota, the United States and the counties around Fall River County, 2006 to 2015, laboratory
AreaTestsAt or above 4 pCi/LMedian
South Dakota, pooled63 counties, pooled4,89358.8%Not pooled
United States, pooled2,669 counties, pooled1,805,52836.3%Not pooled
Bon Homme Countyhighest in the state3979.5%8.1 pCi/L
Davison Countylowest in the state7147.9%3.7 pCi/L
Custer County, SDborders it8268.3%7.2 pCi/L
Dawes County, NEborders it54356.9%4.6 pCi/L
Sioux County, NEborders it2532.0%2.1 pCi/L
Niobrara County, WYborders it1225.0%3.5 pCi/L
The nearest South Dakota counties to Fall River County with 30 or more tests, 2006 to 2015, laboratory
CountyDistanceTestsAt or above 4 pCi/LMedian
Custer County30 mi8268.3%7.2 pCi/L
Pennington County63 mi78651.8%4.3 pCi/L
Lawrence County78 mi12460.5%5.3 pCi/L
Meade County100 mi11254.5%4.1 pCi/L
Hughes County194 mi3066.7%5.5 pCi/L
Brule County226 mi3262.5%6.3 pCi/L
Edmunds County261 mi6861.8%5.0 pCi/L
Davison County272 mi7147.9%3.7 pCi/L
Fall River 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 20172462.5%5.8 pCi/L22.3 pCi/L58.5%+12.5 points
2007 to 20162250.0%4.0 pCi/L22.3 pCi/L57.4%−4.5 points
2006 to 20152254.5%4.3 pCi/L22.3 pCi/L58.8%−2.6 points
2005 to 20142157.1%4.5 pCi/L22.3 pCi/L59.6%First on file

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

Fall River County, Geology

The ground under Fall River County

Predicted

USGS's geologic map splits Fall River County: 63.4% of its land is moderate radon potential and 36.6% high. The map puts 54.9% of Fall River County in the area it calls Pierre Hills and 36.5% in Black Hills, with one smaller area beside them. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 14, in the high band (12 to 17).

USGS's geologic areas under Fall River County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Pierre HillsPierre Shale and Fox Hills sandstone.Moderate1054.9%
Black HillsSandstones and shales of Cretaceous age that surround the Black Hills.High1436.5%
Black HillsLate Paleozoic sedimentary or Precambrian intrusive igneous rocks.Moderate118.2%

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

Fall River County beside the ground around it

South Dakota as a whole has more high-potential ground than Fall River County: 56.7% of its land, against 36.6% here. Of the 5 counties that border it, none has as large a share of high-potential ground; Dawes County, NE comes nearest at 34.0%.

Share of land by USGS radon potential: Fall River County, the 5 counties bordering it and South Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Fall River CountyZone 2None63.4%36.6%
Custer CountyZone 2None88.4%11.6%
Dawes County, NEZone 2None66.0%34.0%
Sioux County, NEZone 2None88.0%12.0%
Niobrara County, WYZone 1None69.5%30.5%
Oglala Lakota CountyZone 21.9%98.1%None
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

Fall River County, Local resources

Radon testing and mitigation in Fall River County

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

What it means

Fall River County, Questions

Questions about radon in Fall River County

Are radon levels high in Fall River County?

Over the 2008 to 2017 laboratory totals, 62.5% of the radon tests reported to CDC for Fall River County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.8 pCi/L. Of the counties bordering it, 2 have a figure over the 2006 to 2015 laboratory totals: Custer County reported the largest share at or above 4 pCi/L, 68.3%, and Dawes County, NE the smallest, 56.9%.

Which counties border Fall River County?

Fall River County borders 5 counties: Custer County, SD, Dawes County, NE, Sioux County, NE, Niobrara County, WY and Oglala Lakota County, SD.

Products

Fall River County, Products

Testing a home in Fall River County

No CDC figure names Fall River County; the nearest county with one, Custer County (30 miles away), reported 68.3% of its tests at or above 4 pCi/L over the 2006 to 2015 laboratory totals, the only reading nearby until a test of this home. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Fall River County; a long-term test tells the year-round average.

Test kits and monitors3

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Best radon monitors for Fall River County homes, compared

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Fall River County, Bordering counties

Counties bordering Fall River County

Calculated by Radon411

Fall River County, Cities and towns

Cities and towns in Fall River County

Fall River County is growing: the Census Bureau puts it at 7,467 residents on July 1, 2025, up 7.1% from 6,971 in 2020. Spread over its land, that is 4.3 people to the square mile. Its largest town, Hot Springs, has 3,670 residents, 49.1% of the total. Together its 3 incorporated places hold 61.2% of those residents; the other 38.8% live outside any of them. Reported testing is thin here: 24 tests over 2008 to 2017, or 3.2 for every 1,000 residents (2025 estimate), where South Dakota as a whole comes to 6.7.

From Hot Springs to Oelrichs, CDC publishes no figure by town: each reads Fall River County's.

The cities and towns in Fall River County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Hot Springs3,670+8.1%49.1%
Edgemont770+5.5%10.3%
Oelrichs127+7.6%1.7%

3 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).

Fall River County, Homes

Homes in Fall River County

Of Fall River County's 4,101 homes, 71% are detached houses, against 67% across South Dakota; 13% are mobile homes. The homes are older than South Dakota's as a whole: half were built before 1971 (1979 for South Dakota), and 44% date from before 1960. Owners live in 75% of the occupied homes (South Dakota: 69%), so for most households a test and a fix are their own to order.

Homes in Fall River County, South Dakota, 2019 to 2023
HomesFall River CountySouth Dakota
Housing units4,101402,364
Detached houses71%67%
In buildings of 5 or more10%16%
Mobile homes13%8%
Built before 196044%29%
Built since 200020%28%
Middle year built19711979
Owner-occupied75%69%

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