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 Lake County, South Dakota
EPA puts Lake County in Zone 1, its highest radon zone, and high results are common there: 76.0% of the 50 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
Share at 4+ pCi/L
76.0%
17.5 pts above SD
- Lake
- 76.0%
- SD
- 58.5%
50 tests, 2008 to 2017
Median result
8.5pCi/L
Action level reached
- Lake
- 8.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
50
19th of 23 by tests
- Lake
- 50
- Minnehaha
- 1,920
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in SD
1 of 23
Top quarter
- Lake
- 76.0%
- Lake
- 76.0%
By share, of 23 with 30+ tests
Read a result for Lake County
Starts at Lake County's median, 8.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 8.5 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. Lake County's median reported result, 2008 to 2017.
The data
Lake County, At a glance
Lake County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Lake 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 Lake County, 2008 to 2017, laboratory
Under 2 pCi/L: 12%2 to 4 pCi/L: 12%4 pCi/L and above: 76%
Of 50 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 6 | 12.0% |
| 2 to 4 pCi/L | 6 | 12.0% |
| 4 pCi/L and above | 38 | 76.0% |
What these figures count
These are the 50 tests reported to CDC for Lake 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).
Lake County, Compared
Lake County radon figures, compared
Calculated by Radon411More than half: 76.0% of the 50 radon tests reported to CDC for Lake County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 1st of 23 South Dakota counties with 30 or more tests for the same period. That is 17.5 points above the 58.5% pooled from 62 South Dakota counties.
The median result, 8.5 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 47.1 pCi/L. The rest split 12.0% under 2 pCi/L and 12.0% 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 76.0% share point the same way here.
No bordering county with a figure for the same period reported a higher share; the closest is Brookings County at 68.5%, the lowest McCook County at 50.0%. Statewide for the same period, Bon Homme County reported the highest share (74.2%) and Davison County the lowest (48.8%).
CDC's ten-year totals for Lake County went from 38 tests (2005 to 2014) to 50 (2008 to 2017), the share going from 73.7% to 76.0%.
Nationally, every county with a figure for the same period pools to 35.7%; Lake County sits 40.3 points above it.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Lake County, Geology
The ground under Lake County
PredictedUSGS's geologic map puts all of Lake County's mapped land in one class: high radon potential. 97.8% 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 | 97.8% |
| Loess-Covered Drift Plains | Pre-Illinoian and Illinoian glacial deposits, and loess. | High | 13 | 2.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Lake County beside the ground around it
Lake 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; Brookings County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Lake County, Local resources
Radon testing and mitigation in Lake 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
Lake County, Questions
Questions about radon in Lake County
Are radon levels high in Lake County?
Over the 2008 to 2017 laboratory totals, 76.0% of the radon tests reported to CDC for Lake County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 8.5 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 58.5%.
Which counties border Lake County?
Lake County borders 6 counties: Moody County, Miner County, McCook County, Brookings County, Minnehaha County and Kingsbury County.
Products
Lake County, Products
Testing a home in Lake County
In Lake County, 76.0% of 50 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 Lake 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
Monitor
Corentium Home 2 battery digital radon monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Screen, app
Method: Alpha spectrometry
Readings: Every 60 minutes
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
Lake County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Lake County
Explore
Lake County, Bordering counties
Counties bordering Lake County
Calculated by Radon411- Radon levels in Moody CountyEPA zone 1
70.0%at or above 4 pCi/L
Median 6.2 pCi/L · 20 tests · 6.0 points below Lake County
- Radon levels in Brookings CountyEPA zone 1
68.5%at or above 4 pCi/L
Median 6.6 pCi/L · 356 tests · 7.5 points below Lake County
- Radon levels in Kingsbury CountyEPA zone 1
68.2%at or above 4 pCi/L
Median 7.4 pCi/L · 44 tests · 7.8 points below Lake County
- Radon levels in Minnehaha CountyEPA zone 1
58.5%at or above 4 pCi/L
Median 4.8 pCi/L · 1,920 tests · 17.5 points below Lake County
- Radon levels in Miner CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 3.9 pCi/L · 4 tests · 26.0 points below Lake County
- Radon levels in McCook CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 3.9 pCi/L · 30 tests · 26.0 points below Lake County
Lake County, Cities and towns
Cities and towns in Lake County
Lake County's population has barely moved since 2020: 10,993 residents on July 1, 2025 against 11,015 then, by the Census Bureau's estimates. That works out to 20 people per square mile of land. Madison alone is home to 6,065 of them, 55.2% of the total. Together its 5 incorporated places hold 59.1% of those residents; the other 40.9% live outside any of them. CDC's 50 reported tests for 2008 to 2017 work out to 4.5 per 1,000 residents (2025 estimate), close to South Dakota's 6.7.
From Madison to Nunda, CDC publishes no figure by town: each reads Lake County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Madison | 6,065 | −1.5% | 55.2% |
| Wentworth | 172 | −5.0% | 1.6% |
| Ramona | 163 | +1.2% | 1.5% |
| Brant Lake | 56 | −3.4% | 0.5% |
| Nunda | 46 | +2.2% | 0.4% |
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).
Lake County, Homes
Homes in Lake County
Of Lake County's 5,747 homes, 73% are detached houses, against 67% across South Dakota; 12% are in buildings of five or more homes. Half of its homes were built before 1976, close to South Dakota's 1979: 32% date from before 1960 and 21% from 2000 or later. 71% 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 | Lake County | South Dakota |
|---|---|---|
| Housing units | 5,747 | 402,364 |
| Detached houses | 73% | 67% |
| In buildings of 5 or more | 12% | 16% |
| Mobile homes | 7% | 8% |
| Built before 1960 | 32% | 29% |
| Built since 2000 | 21% | 28% |
| Middle year built | 1976 | 1979 |
| Owner-occupied | 71% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.