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Radon Levels in Brown County, South Dakota

EPA puts Brown County in Zone 1, its highest radon zone, and high results are common there: 71.0% of the 62 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

    71.0%

    12.5 pts above SD

    Brown
    71.0%
    SD
    58.5%

    62 tests, 2008 to 2017

  • Median result

    5.9pCi/L

    Action level reached

    Brown
    5.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    62

    16th of 23 by tests

    Brown
    62
    Minnehaha
    1,920

    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 SD

    4 of 23

    Top quarter

    Brown
    71.0%
    Lake
    76.0%

    By share, of 23 with 30+ tests

Read a result for Brown County

Starts at Brown County's median, 5.9 pCi/L

5.9pCi/L

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

EPA’s reading of 5.9 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. Brown County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Brown County, At a glance

Brown County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Brown 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 Brown County, 2008 to 2017, laboratory

Reported results by concentration band, Brown County, 2008 to 2017, laboratory
Under 2 pCi/L: 8%2 to 4 pCi/L: 21%4 pCi/L and above: 71%

Of 62 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Brown County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L58.1%
2 to 4 pCi/L1321.0%
4 pCi/L and above4471.0%
What these figures count

These are the 62 tests reported to CDC for Brown 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

Brown County, Compared

Brown County radon figures, compared

Calculated by Radon411

More than half: 71.0% of the 62 radon tests reported to CDC for Brown County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 4th of 23 South Dakota counties with 30 or more tests for the same period. That is 12.5 points above the 58.5% pooled from 62 South Dakota counties.

The median result, 5.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 18.8 pCi/L. The rest split 8.1% under 2 pCi/L and 21.0% from 2 to 4 (South Dakota: 23.6% and 17.9%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 71.0% share point the same way here.

Dickey County, ND, the one bordering county with a figure for the same period, reported 67.1%. 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 Brown County went from 46 tests (2005 to 2014) to 62 (2008 to 2017), the share going from 56.5% to 71.0%.

Nationally, every county with a figure for the same period pools to 35.7%; Brown County sits 35.3 points above it.

Brown County against South Dakota, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Brown County
Brown County6271.0%5.9 pCi/LThis county
South Dakota, pooled62 counties, pooled6,27558.5%Not pooled−12.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−35.3 points
Lake Countyhighest in the state5076.0%8.5 pCi/L+5.0 points
Davison Countylowest in the state8448.8%3.8 pCi/L−22.2 points
Faulk County, SDborders it1100.0%32.2 pCi/L+29.0 points
Marshall County, SDborders it1681.3%10.5 pCi/L+10.3 points
Sargent County, NDborders it2475.0%7.2 pCi/L+4.0 points
Dickey County, NDborders it7067.1%4.8 pCi/L−3.9 points
Edmunds County, SDborders it1266.7%5.9 pCi/L−4.3 points
McPherson County, SDborders it1258.3%4.8 pCi/L−12.7 points
Day County, SDborders it1154.5%4.5 pCi/L−16.5 points
Spink County, SDborders it2450.0%3.8 pCi/L−21.0 points
Where Brown County's reported results fell, 2008 to 2017, laboratory, beside South Dakota and the United States
ResultBrown County testsBrown County shareSouth Dakota shareU.S. shareAgainst South Dakota
Under 2 pCi/L58.1%23.6%39.6%−15.5 points
2 to 4 pCi/L1321.0%17.9%24.7%+3.1 points
4 pCi/L and above4471.0%58.5%35.7%+12.5 points
Brown 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
Lake County1 of 235076.0%8.5 pCi/L
Bon Homme County2 of 236274.2%7.2 pCi/L
Yankton County3 of 2311872.9%6.3 pCi/L
Brown County4 of 236271.0%5.9 pCi/L
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
Brown 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 20176271.0%5.9 pCi/L18.8 pCi/L58.5%+7.6 points
2007 to 20164163.4%4.5 pCi/L16.4 pCi/L57.4%+3.8 points
2006 to 20155259.6%4.4 pCi/L17.0 pCi/L58.8%+3.1 points
2005 to 20144656.5%4.3 pCi/L17.0 pCi/L59.6%First on file

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

Brown County, Geology

The ground under Brown County

Predicted

USGS's geologic map puts all of Brown County's mapped land in one class: high radon potential. The map puts 50.1% of Brown County in the area it calls Missouri Coteau/James River Lowland/Coteau des Prairies and 49.8% in Glacial Lake Dakota. USGS gives both a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Brown County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Missouri Coteau/James River Lowland/Coteau des PrairiesGlacial drift derived largely from Cretaceous marine shale.High1450.1%
Glacial Lake DakotaSilt and clay glacial lake deposits.High1449.8%

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

Brown County beside the ground around it

Brown County has more high-potential ground than South Dakota as a whole: 100% of its land against 56.7%. Of the 8 counties that border it, none has as large a share of high-potential ground; Dickey County, ND comes nearest at 100%.

Share of land by USGS radon potential: Brown County, the 8 counties bordering it and South Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Brown CountyZone 1NoneNone100%
Dickey County, NDZone 1NoneNone100%
Day CountyZone 1NoneNone100%
Marshall CountyZone 1NoneNone100%
Spink CountyZone 1NoneNone100%
Edmunds CountyZone 1NoneNone100%
McPherson CountyZone 1NoneNone100%
Sargent County, NDZone 1NoneNone100%
Faulk CountyZone 1NoneNone100%
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

Brown County, Local resources

Radon testing and mitigation in Brown County

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

What it means

Brown County, Questions

Questions about radon in Brown County

Are radon levels high in Brown County?

Over the 2008 to 2017 laboratory totals, 71.0% of the radon tests reported to CDC for Brown County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.9 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, 3 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Brown County?

Brown County borders 8 counties: Dickey County, ND, Day County, SD, Marshall County, SD, Spink County, SD, Edmunds County, SD, McPherson County, SD, Sargent County, ND and Faulk County, SD.

Products

Brown County, Products

Testing a home in Brown County

In Brown County, 71.0% of 62 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across South Dakota. In Zone 1 the year-round level in Brown 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

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

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Brown County, Bordering counties

Counties bordering Brown County

Calculated by Radon411

Brown County, Cities and towns

Cities and towns in Brown County

About 37,561 people live in Brown County by the Census Bureau's estimate for July 1, 2025, 669 fewer than in 2020 (−1.7%). That works out to 22 people per square mile of land. Aberdeen alone is home to 27,961 of them, 74.4% of the total. Together its 10 incorporated places hold 81.3% of those residents; the other 18.7% live outside any of them. Reported testing is thin here: 62 tests over 2008 to 2017, or 1.7 for every 1,000 residents (2025 estimate), where South Dakota as a whole comes to 6.7.

From Aberdeen to Verdon, CDC publishes no figure by town: each reads Brown County's.

The cities and towns in Brown County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Aberdeen27,961−1.6%74.4%
Groton1,337−3.3%3.6%
Warner449−5.1%1.2%
Frederick205−3.3%0.5%
Hecla190−4.0%0.5%
Columbia155−1.3%0.4%
Claremont107−1.8%0.3%
Westport81−4.7%0.2%
Stratford58−1.7%0.2%
Verdon6LevelUnder 0.1%

10 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).

Brown County, Homes

Homes in Brown County

Of Brown County's 18,009 homes, 62% are detached houses, against 67% across South Dakota; 23% are in buildings of five or more homes. Half of its homes were built before 1974, close to South Dakota's 1979: 34% date from before 1960 and 22% from 2000 or later. 66% of occupied homes are lived in by their owner (South Dakota: 69%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Brown County, South Dakota, 2019 to 2023
HomesBrown CountySouth Dakota
Housing units18,009402,364
Detached houses62%67%
In buildings of 5 or more23%16%
Mobile homes6%8%
Built before 196034%29%
Built since 200022%28%
Middle year built19741979
Owner-occupied66%69%

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