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Radon Levels in Bon Homme County, South Dakota

EPA puts Bon Homme County in Zone 1, its highest radon zone, and high results are common there: 74.2% 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

    74.2%

    15.7 pts above SD

    Bon Homme
    74.2%
    SD
    58.5%

    62 tests, 2008 to 2017

  • Median result

    7.2pCi/L

    Action level reached

    Bon Homme
    7.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    62

    15th of 23 by tests

    Bon Homme
    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

    2 of 23

    Top quarter

    Bon Homme
    74.2%
    Lake
    76.0%

    By share, of 23 with 30+ tests

Read a result for Bon Homme County

Starts at Bon Homme County's median, 7.2 pCi/L

7.2pCi/L

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

EPA’s reading of 7.2 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. Bon Homme County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Bon Homme County, At a glance

Bon Homme County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Bon Homme 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 Bon Homme County, 2008 to 2017, laboratory

Reported results by concentration band, Bon Homme County, 2008 to 2017, laboratory
Under 2 pCi/L: 11%2 to 4 pCi/L: 15%4 pCi/L and above: 74%

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

Reported results by concentration band, Bon Homme County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L711.3%
2 to 4 pCi/L914.5%
4 pCi/L and above4674.2%
What these figures count

These are the 62 tests reported to CDC for Bon Homme 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

Bon Homme County, Compared

Bon Homme County radon figures, compared

Calculated by Radon411

More than half: 74.2% of the 62 radon tests reported to CDC for Bon Homme County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 2nd of 23 South Dakota counties with 30 or more tests for the same period. That is 15.7 points above the 58.5% pooled from 62 South Dakota counties.

The median result, 7.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 34.4 pCi/L. The rest split 11.3% under 2 pCi/L and 14.5% 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 74.2% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is Yankton County at 72.9%, the lowest Hutchinson County at 66.7%. 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 Bon Homme County went from 26 tests (2005 to 2014) to 62 (2008 to 2017), the share going from 73.1% to 74.2%.

Nationally, every county with a figure for the same period pools to 35.7%; Bon Homme County sits 38.5 points above it.

Bon Homme County against South Dakota, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Bon Homme County
Bon Homme County6274.2%7.2 pCi/LThis county
South Dakota, pooled62 counties, pooled6,27558.5%Not pooled−15.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−38.5 points
Lake Countyhighest in the state5076.0%8.5 pCi/L+1.8 points
Davison Countylowest in the state8448.8%3.8 pCi/L−25.4 points
Yankton County, SDborders it11872.9%6.3 pCi/L−1.3 points
Knox County, NEborders it40168.8%6.2 pCi/L−5.4 points
Hutchinson County, SDborders it3966.7%5.8 pCi/L−7.5 points
Charles Mix County, SDborders it2860.7%6.5 pCi/L−13.5 points
Where Bon Homme County's reported results fell, 2008 to 2017, laboratory, beside South Dakota and the United States
ResultBon Homme County testsBon Homme County shareSouth Dakota shareU.S. shareAgainst South Dakota
Under 2 pCi/L711.3%23.6%39.6%−12.3 points
2 to 4 pCi/L914.5%17.9%24.7%−3.4 points
4 pCi/L and above4674.2%58.5%35.7%+15.7 points
Bon Homme 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
Bon Homme 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 20176274.2%7.2 pCi/L34.4 pCi/L58.5%−4.9 points
2007 to 20164379.1%8.0 pCi/L34.4 pCi/L57.4%−0.4 points
2006 to 20153979.5%8.1 pCi/L34.4 pCi/L58.8%+6.4 points
2005 to 20142673.1%6.5 pCi/L34.4 pCi/L59.6%First on file

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

Bon Homme County, Geology

The ground under Bon Homme County

Predicted

USGS's geologic map puts all of Bon Homme County's mapped land in one class: high radon potential. 99.5% of it lies in the area the map calls Missouri Coteau/James River Lowland/Coteau des Prairies, to which USGS gives a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Bon Homme 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.High1499.5%
Sharon SpringsCretaceous Pierre Shale bedrock, including the uranium-bearing Sharon Springs Member.High120.5%

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

Bon Homme County beside the ground around it

Bon Homme County has more high-potential ground than South Dakota as a whole: 100% of its land against 56.7%. Of the 4 counties that border it, none has as large a share of high-potential ground; Hutchinson County comes nearest at 100%.

Share of land by USGS radon potential: Bon Homme County, the 4 counties bordering it and South Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Bon Homme CountyZone 1NoneNone100%
Knox County, NEZone 1None20.0%80.0%
Yankton CountyZone 1NoneNone100%
Hutchinson CountyZone 1NoneNone100%
Charles Mix CountyZone 1None0.2%99.8%
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

Bon Homme County, Local resources

Radon testing and mitigation in Bon Homme County

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

What it means

Bon Homme County, Questions

Questions about radon in Bon Homme County

Are radon levels high in Bon Homme County?

Over the 2008 to 2017 laboratory totals, 74.2% of the radon tests reported to CDC for Bon Homme County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 7.2 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, 1 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Bon Homme County?

Bon Homme County borders 4 counties: Knox County, NE, Yankton County, SD, Hutchinson County, SD and Charles Mix County, SD.

Products

Bon Homme County, Products

Testing a home in Bon Homme County

In Bon Homme County, 74.2% 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 Bon Homme 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

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

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Bon Homme County, Bordering counties

Counties bordering Bon Homme County

Calculated by Radon411

Bon Homme County, Cities and towns

Cities and towns in Bon Homme County

The Census Bureau estimates 7,244 residents in Bon Homme County for July 1, 2025, 263 more than in 2020 (+3.8%). That works out to 13 people per square mile of land. Its largest town, Springfield, has 1,926 residents, 26.6% of the total. Together its 5 incorporated places hold 67.4% of those residents; the other 32.6% live outside any of them. CDC's 62 reported tests for 2008 to 2017 work out to 8.6 per 1,000 residents (2025 estimate), close to South Dakota's 6.7.

From Springfield to Tabor, CDC publishes no figure by town: each reads Bon Homme County's.

The cities and towns in Bon Homme County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Springfield1,926+0.6%26.6%
Tyndall1,117+6.2%15.4%
Scotland804+1.9%11.1%
Avon623+5.6%8.6%
Tabor413+1.7%5.7%

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).

Bon Homme County, Homes

Homes in Bon Homme County

Bon Homme County is a place of houses on their own lots: 87% of its 2,823 homes are detached single-family houses, against 67% across South Dakota. The homes are older than South Dakota's as a whole: half were built before 1957 (1979 for South Dakota), and 53% date from before 1960. Owners live in 78% of the occupied homes (South Dakota: 69%), so for most households a test and a fix are their own to order.

Homes in Bon Homme County, South Dakota, 2019 to 2023
HomesBon Homme CountySouth Dakota
Housing units2,823402,364
Detached houses87%67%
In buildings of 5 or more6%16%
Mobile homes5%8%
Built before 196053%29%
Built since 20008%28%
Middle year built19571979
Owner-occupied78%69%

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