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Radon Levels in Codington County, South Dakota

EPA puts Codington County in Zone 1, its highest radon zone, and high results are common there: 64.9% of the 77 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

    64.9%

    6.4 pts above SD

    Codington
    64.9%
    SD
    58.5%

    77 tests, 2008 to 2017

  • Median result

    5.8pCi/L

    Action level reached

    Codington
    5.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    77

    13th of 23 by tests

    Codington
    77
    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

    11 of 23

    Middle half

    Codington
    64.9%
    Lake
    76.0%

    By share, of 23 with 30+ tests

Read a result for Codington County

Starts at Codington County's median, 5.8 pCi/L

5.8pCi/L

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

EPA’s reading of 5.8 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. Codington County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Codington County, At a glance

Codington County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Codington County, 2008 to 2017, laboratory
Under 2 pCi/L: 25%2 to 4 pCi/L: 10%4 pCi/L and above: 65%

Of 77 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Codington County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1924.7%
2 to 4 pCi/L810.4%
4 pCi/L and above5064.9%
What these figures count

These are the 77 tests reported to CDC for Codington 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

Codington County, Compared

Codington County radon figures, compared

Calculated by Radon411

More than half: 64.9% of the 77 radon tests reported to CDC for Codington County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 11th of 23 South Dakota counties with 30 or more tests for the same period. That is 6.4 points above the 58.5% pooled from 62 South Dakota counties.

The median result, 5.8 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 57.1 pCi/L. The rest split 24.7% under 2 pCi/L and 10.4% 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 64.9% share point the same way here.

Grant County, the one bordering county with a figure for the same period, reported 55.1%. 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 Codington County went from 64 tests (2005 to 2014) to 77 (2008 to 2017), the share going from 62.5% to 64.9%.

Nationally, every county with a figure for the same period pools to 35.7%; Codington County sits 29.2 points above it.

Codington County against South Dakota, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Codington County
Codington County7764.9%5.8 pCi/LThis county
South Dakota, pooled62 counties, pooled6,27558.5%Not pooled−6.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−29.2 points
Lake Countyhighest in the state5076.0%8.5 pCi/L+11.1 points
Davison Countylowest in the state8448.8%3.8 pCi/L−16.1 points
Clark County, SDborders it977.8%5.9 pCi/L+12.9 points
Hamlin County, SDborders it1376.9%6.3 pCi/L+12.0 points
Deuel County, SDborders it2576.0%6.2 pCi/L+11.1 points
Grant County, SDborders it7855.1%5.0 pCi/L−9.8 points
Day County, SDborders it1154.5%4.5 pCi/L−10.4 points
Where Codington County's reported results fell, 2008 to 2017, laboratory, beside South Dakota and the United States
ResultCodington County testsCodington County shareSouth Dakota shareU.S. shareAgainst South Dakota
Under 2 pCi/L1924.7%23.6%39.6%+1.1 points
2 to 4 pCi/L810.4%17.9%24.7%−7.5 points
4 pCi/L and above5064.9%58.5%35.7%+6.4 points
Codington 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
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
Lincoln County16 of 2379556.5%4.7 pCi/L
Codington 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 20177764.9%5.8 pCi/L57.1 pCi/L58.5%+4.2 points
2007 to 20165660.7%5.8 pCi/L57.1 pCi/L57.4%−4.6 points
2006 to 20157265.3%6.0 pCi/L57.1 pCi/L58.8%+2.8 points
2005 to 20146462.5%6.0 pCi/L57.1 pCi/L59.6%First on file

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

Codington County, Geology

The ground under Codington County

Predicted

USGS's geologic map puts all of Codington County's mapped land in one class: high radon potential. The map puts 94.0% of Codington County in the area it calls Missouri Coteau/James River Lowland/Coteau des Prairies and 6.0% in Loess-Covered Drift Plains. USGS gives the first a radon index of 14 and the second 13, both in the high band (12 to 17).

USGS's geologic areas under Codington 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.High1494.0%
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High136.0%

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

Codington County beside the ground around it

Codington County has more high-potential ground than South Dakota as a whole: 100% of its land against 56.7%. Of the 5 counties that border it, none has as large a share of high-potential ground; Clark County comes nearest at 100%.

Share of land by USGS radon potential: Codington County, the 5 counties bordering it and South Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Codington CountyZone 1NoneNone100%
Grant CountyZone 1NoneNone100%
Hamlin CountyZone 1NoneNone100%
Clark CountyZone 1NoneNone100%
Day CountyZone 1NoneNone100%
Deuel 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

Codington County, Local resources

Radon testing and mitigation in Codington County

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

What it means

Codington County, Questions

Questions about radon in Codington County

Are radon levels high in Codington County?

Over the 2008 to 2017 laboratory totals, 64.9% of the radon tests reported to CDC for Codington County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.8 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, 10 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Codington County?

Codington County borders 5 counties: Grant County, Hamlin County, Clark County, Day County and Deuel County.

Products

Codington County, Products

Testing a home in Codington County

In Codington County, 64.9% of 77 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 Codington 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

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

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Codington County, Bordering counties

Counties bordering Codington County

Calculated by Radon411

Codington County, Cities and towns

Cities and towns in Codington County

The Census Bureau estimates 29,562 residents in Codington County for July 1, 2025, 1,209 more than in 2020 (+4.3%). That works out to 43 people per square mile of land. Watertown alone is home to 23,736 of them, 80.3% of the total. Together its 6 incorporated places hold 83.9% of those residents; the other 16.1% live outside any of them. Reported testing is thin here: 77 tests over 2008 to 2017, or 2.6 for every 1,000 residents (2025 estimate), where South Dakota as a whole comes to 6.7.

From Watertown to Wallace, CDC publishes no figure by town: each reads Codington County's.

The cities and towns in Codington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Watertown23,736+4.7%80.3%
Florence338+0.9%1.1%
Henry266+3.9%0.9%
South Shore189−0.5%0.6%
Kranzburg166+1.8%0.6%
Wallace95+1.1%0.3%

6 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).

Codington County, Homes

Homes in Codington County

Of Codington County's 13,388 homes, 69% are detached houses, against 67% across South Dakota; 13% are in buildings of five or more homes. Half of its homes were built before 1979, close to South Dakota's 1979: 30% date from before 1960 and 26% from 2000 or later. 67% 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 Codington County, South Dakota, 2019 to 2023
HomesCodington CountySouth Dakota
Housing units13,388402,364
Detached houses69%67%
In buildings of 5 or more13%16%
Mobile homes7%8%
Built before 196030%29%
Built since 200026%28%
Middle year built19791979
Owner-occupied67%69%

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