Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Grant County, South Dakota
EPA puts Grant County in Zone 1, its highest radon zone, and high results are common there: 55.1% of the 78 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
55.1%
3.4 pts below SD
- Grant
- 55.1%
- SD
- 58.5%
78 tests, 2008 to 2017
Median result
5.0pCi/L
Action level reached
- Grant
- 5.0 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
78
12th of 23 by tests
- Grant
- 78
- 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
17 of 23
Middle half
- Grant
- 55.1%
- Lake
- 76.0%
By share, of 23 with 30+ tests
Read a result for Grant County
Starts at Grant County's median, 5.0 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 5.0 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. Grant County's median reported result, 2008 to 2017.
The data
Grant County, At a glance
Grant County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Grant 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 Grant County, 2008 to 2017, laboratory
Under 2 pCi/L: 36%2 to 4 pCi/L: 9%4 pCi/L and above: 55%
Of 78 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 28 | 35.9% |
| 2 to 4 pCi/L | 7 | 9.0% |
| 4 pCi/L and above | 43 | 55.1% |
What these figures count
These are the 78 tests reported to CDC for Grant 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).
Grant County, Compared
Grant County radon figures, compared
Calculated by Radon411More than half: 55.1% of the 78 radon tests reported to CDC for Grant County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 17th of 23 South Dakota counties with 30 or more tests for the same period. That is 3.4 points below the 58.5% pooled from 62 South Dakota counties.
The median result, 5.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 28.0 pCi/L. The rest split 35.9% under 2 pCi/L and 9.0% 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 55.1% share point the same way here.
All 3 of its bordering counties with figures ran higher, led by Big Stone County, MN at 67.0%; the lowest of them, Lac qui Parle County, MN, reported 63.5%. 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 Grant County went from 83 tests (2005 to 2014) to 78 (2008 to 2017), the share going from 61.4% to 55.1%.
Nationally, every county with a figure for the same period pools to 35.7%; Grant County sits 19.4 points above it. CDC also counts 9 tests taken after mitigation in Grant County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Grant County, Geology
The ground under Grant County
PredictedUSGS's geologic map puts all of Grant 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 | 99.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Grant County beside the ground around it
Grant 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; Big Stone County, MN comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Grant County, Local resources
Radon testing and mitigation in Grant 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
Grant County, Questions
Questions about radon in Grant County
Are radon levels high in Grant County?
Over the 2008 to 2017 laboratory totals, 55.1% of the radon tests reported to CDC for Grant County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.0 pCi/L. Of 23 South Dakota counties with 30 or more tests for the same period, 16 reported a higher share; pooled, the state comes to 58.5%.
Which counties border Grant County?
Grant County borders 6 counties: Codington County, SD, Big Stone County, MN, Lac qui Parle County, MN, Deuel County, SD, Roberts County, SD and Day County, SD.
Products
Grant County, Products
Testing a home in Grant County
In Grant County, 55.1% of 78 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 Grant 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
Wave Plus battery radon and air quality monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- App only
Method: Alpha spectrometry
Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Grant County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Grant County
Explore
Grant County, Bordering counties
Counties bordering Grant County
Calculated by Radon411- Radon levels in Deuel County, SDEPA zone 1
76.0%at or above 4 pCi/L
Median 6.2 pCi/L · 25 tests · 20.9 points above Grant County
- Radon levels in Big Stone County, MNEPA zone 1
67.0%at or above 4 pCi/L
Median 5.0 pCi/L · 182 tests · 11.9 points above Grant County
- Radon levels in Codington County, SDEPA zone 1
64.9%at or above 4 pCi/L
Median 5.8 pCi/L · 77 tests · 9.8 points above Grant County
- Radon levels in Lac qui Parle County, MNEPA zone 1
63.5%at or above 4 pCi/L
Median 5.3 pCi/L · 211 tests · 8.4 points above Grant County
- Radon levels in Day County, SDEPA zone 1
54.5%at or above 4 pCi/L
Median 4.5 pCi/L · 11 tests · 0.6 points below Grant County
- Radon levels in Roberts County, SDEPA zone 1
46.2%at or above 4 pCi/L
Median 3.8 pCi/L · 26 tests · 8.9 points below Grant County
Grant County, Cities and towns
Cities and towns in Grant County
Grant County's population has barely moved since 2020: 7,534 residents on July 1, 2025 against 7,537 then, by the Census Bureau's estimates. That works out to 11 people per square mile of land. Its largest town, Milbank, has 3,512 residents, 46.6% of the total. Together its 9 incorporated places hold 57.3% of those residents; the other 42.7% live outside any of them. Testing is reported here more often than across the state: CDC's 78 reported tests for 2008 to 2017 come to 10.4 for every 1,000 residents (2025 estimate), against 6.7 for South Dakota.
From Milbank to Albee, CDC publishes no figure by town: each reads Grant County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Milbank | 3,512 | −0.5% | 46.6% |
| Big Stone City | 406 | −1.0% | 5.4% |
| Stockholm | 102 | +2.0% | 1.4% |
| Revillo | 96 | −2.0% | 1.3% |
| Strandburg | 65 | Level | 0.9% |
| La Bolt | 62 | Level | 0.8% |
| Twin Brooks | 47 | Level | 0.6% |
| Marvin | 19 | +5.6% | 0.3% |
| Albee | 8 | Level | 0.1% |
9 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).
Grant County, Homes
Homes in Grant County
Grant County is a place of houses on their own lots: 78% of its 3,441 homes are detached single-family houses, against 67% across South Dakota. Half of its homes were built before 1974, close to South Dakota's 1979: 36% date from before 1960 and 17% from 2000 or later. 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 | Grant County | South Dakota |
|---|---|---|
| Housing units | 3,441 | 402,364 |
| Detached houses | 78% | 67% |
| In buildings of 5 or more | 7% | 16% |
| Mobile homes | 5% | 8% |
| Built before 1960 | 36% | 29% |
| Built since 2000 | 17% | 28% |
| Middle year built | 1974 | 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.