Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Clark County, South Dakota
EPA puts Clark County in Zone 1, its highest radon zone, and only 9 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
Highest bordering
68.8%
Kingsbury County
- Kingsbury
- 68.8%
- Beadle
- 63.0%
3 of 6 neighbours have 30+ tests, 2006 to 2015
Nearest county
65.3%
Codington County, 28 miles
- Codington
- 65.3%
- SD
- 58.8%
Share at 4+ pCi/L, 72 tests, 2006 to 2015
Ground above low
100.0%
1.0 pts above SD
- Clark
- 100.0%
- SD
- 99.0%
Share of land USGS rates moderate or high potential
Tests reported
9
Too few for a share
- Clark
- 9
- Needed
- 30
2008 to 2017, laboratory
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Read a result for Clark County
Starts at EPA's action level
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
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 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.
The data
Clark County, At a glance
Clark County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Clark County in
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 Clark County, 2008 to 2017, laboratory
CDC holds 9 reported tests for Clark County over the 2008 to 2017 laboratory totals, with a median of 5.9 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Clark County beside the counties around it is how this page reads it.
What these figures count
Only 9 tests were reported to CDC for Clark 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).
Clark County, Compared
Clark County radon figures, compared
Calculated by Radon411CDC's largest figure for Clark County rests on 9 tests over the 2008 to 2017 laboratory totals, 7 of them at or above 4 pCi/L, so each test moves its share by 11.1 points and no rank or comparison is drawn from it. Results reached as high as 24.0 pCi/L, with a middle value of 5.9 pCi/L.
Of the counties bordering it, 3 have a figure over the 2006 to 2015 laboratory totals: Kingsbury County reported the largest share at or above 4 pCi/L, 68.8%, and Beadle County the smallest, 63.0%, with Codington County at 65.3% between. Farther out, Grant County (52 miles away) at 64.6%, Brookings County (57 miles away) at 67.4% and Brown County (59 miles away) at 59.6% 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 Clark County in Zone 1, the map's highest label: a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clark County, Geology
The ground under Clark County
PredictedUSGS's geologic map puts all of Clark County's mapped land in one class: high radon potential. All 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).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Missouri Coteau/James River Lowland/Coteau des Prairies | Glacial drift derived largely from Cretaceous marine shale. | High | 14 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clark County beside the ground around it
Clark County has more high-potential ground than South Dakota as a whole: 100% of its land against 56.7%. Of the 6 counties that border it, none has as large a share of high-potential ground; Beadle County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Clark County, Local resources
Radon testing and mitigation in Clark County
- South Dakota's radon programDepartment of Agriculture and Natural ResourcesSouth Dakota's radon program offers free or discounted test kits, and answers questions about testing and mitigation in South Dakota.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
The Department of Agriculture and Natural Resources (DANR) will provide 500 free Radon test kits to South Dakota Residents.
- Compare kits
- Professionals in South Dakota5 professionals are listed in South Dakota.
What South Dakota's program says
- Phone
- 1-800-438-3367
What it means
Clark County, Questions
Questions about radon in Clark County
Are radon levels high in Clark County?
Over the 2008 to 2017 laboratory totals, 77.8% of the radon tests reported to CDC for Clark County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.9 pCi/L. Of the counties bordering it, 3 have a figure over the 2006 to 2015 laboratory totals: Kingsbury County reported the largest share at or above 4 pCi/L, 68.8%, and Beadle County the smallest, 63.0%, with Codington County at 65.3% between.
Which counties border Clark County?
Clark County borders 6 counties: Hamlin County, Codington County, Spink County, Kingsbury County, Day County and Beadle County.
Products
Clark County, Products
Testing a home in Clark County
No CDC figure names Clark County; the nearest county with one, Codington County (28 miles away), reported 65.3% 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 1 the year-round level in Clark 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
MonitorAEGTEST
HOUND-1011 rechargeable radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Clark County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Clark County
Explore
Clark County, Bordering counties
Counties bordering Clark County
Calculated by Radon411- Radon levels in Hamlin CountyEPA zone 1
70.6%at or above 4 pCi/L
Median 4.8 pCi/L · 17 tests
- Radon levels in Kingsbury CountyEPA zone 1
68.8%at or above 4 pCi/L
Median 8.4 pCi/L · 32 tests
- Radon levels in Codington CountyEPA zone 1
65.3%at or above 4 pCi/L
Median 6.0 pCi/L · 72 tests
- Radon levels in Beadle CountyEPA zone 1
63.0%at or above 4 pCi/L
Median 5.6 pCi/L · 46 tests
- Radon levels in Spink CountyEPA zone 1
58.8%at or above 4 pCi/L
Median 4.9 pCi/L · 17 tests
- Radon levels in Day CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 4.0 pCi/L · 6 tests
Clark County, Cities and towns
Cities and towns in Clark County
The Census Bureau estimates 4,031 residents in Clark County for July 1, 2025, 181 more than in 2020 (+4.7%). Spread over its land, that is 4.2 people to the square mile. Its largest town, Clark, has 1,183 residents, 29.3% of the total. Together its 7 incorporated places hold 42.4% of those residents; the other 57.6% live outside any of them. Reported testing is thin here: 9 tests over 2008 to 2017, or 2.2 for every 1,000 residents (2025 estimate), where South Dakota as a whole comes to 6.7.
From Clark to Garden City, CDC publishes no figure by town: each reads Clark County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Clark | 1,183 | +3.0% | 29.3% |
| Willow Lake | 271 | +1.9% | 6.7% |
| Bradley | 69 | +4.5% | 1.7% |
| Raymond | 57 | +5.6% | 1.4% |
| Vienna | 54 | +8.0% | 1.3% |
| Naples | 41 | +2.5% | 1.0% |
| Garden City | 36 | +5.9% | 0.9% |
7 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).
Clark County, Homes
Homes in Clark County
Clark County is a place of houses on their own lots: 85% of its 1,609 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 1959 (1979 for South Dakota), and 51% date from before 1960. Owners live in 82% of the occupied homes (South Dakota: 69%), so for most households a test and a fix are their own to order.
| Homes | Clark County | South Dakota |
|---|---|---|
| Housing units | 1,609 | 402,364 |
| Detached houses | 85% | 67% |
| In buildings of 5 or more | 4% | 16% |
| Mobile homes | 9% | 8% |
| Built before 1960 | 51% | 29% |
| Built since 2000 | 13% | 28% |
| Middle year built | 1959 | 1979 |
| Owner-occupied | 82% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.