Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Gregory County, South Dakota
EPA puts Gregory County in Zone 2, its middle radon zone, and only 15 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
63.0%
Boyd County
- Boyd
- 63.0%
1 of 5 neighbours have 30+ tests, 2006 to 2015
Nearest county
62.5%
Brule County, 37 miles
- Brule
- 62.5%
- SD
- 58.8%
Share at 4+ pCi/L, 32 tests, 2006 to 2015
Ground above low
100.0%
1.0 pts above SD
- Gregory
- 100.0%
- SD
- 99.0%
Share of land USGS rates moderate or high potential
Tests reported
15
Too few for a share
- Gregory
- 15
- Needed
- 30
2008 to 2017, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Gregory 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
Gregory County, At a glance
Gregory County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Gregory County is a
USGS geologic potential: Moderate across 93% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Gregory County, 2008 to 2017, laboratory
CDC holds 15 reported tests for Gregory County over the 2008 to 2017 laboratory totals, with a median of 5.3 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Gregory County beside the counties around it is how this page reads it.
What these figures count
Only 15 tests were reported to CDC for Gregory 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).
Gregory County, Compared
Gregory County radon figures, compared
Calculated by Radon411CDC's largest figure for Gregory County rests on 15 tests over the 2008 to 2017 laboratory totals, 10 of them at or above 4 pCi/L, so each test moves its share by 6.7 points and no rank or comparison is drawn from it. Results reached as high as 13.9 pCi/L, with a middle value of 5.3 pCi/L.
Boyd County, NE, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 63.0% of its tests at or above 4 pCi/L. Farther out, Brule County (37 miles away) at 62.5%, Davison County (62 miles away) at 47.9% and Bon Homme County (67 miles away) at 79.5% 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 Gregory County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 93% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Gregory County, Geology
The ground under Gregory County
PredictedMost of the ground under Gregory County is one class on USGS's geologic map: 92.9% of its land is moderate radon potential, with 7.1% high. The map puts 92.9% of Gregory County in the area it calls Pierre Hills and 7.1% in Missouri Coteau/James River Lowland/Coteau des Prairies. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 14, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Pierre Hills | Pierre Shale and Fox Hills sandstone. | Moderate | 10 | 92.9% |
| Missouri Coteau/James River Lowland/Coteau des Prairies | Glacial drift derived largely from Cretaceous marine shale. | High | 14 | 7.1% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Gregory County beside the ground around it
South Dakota as a whole has more high-potential ground than Gregory County: 56.7% of its land, against 7.1% here. Of the 5 counties that border it, 4 have more high-potential ground, Charles Mix County the most at 99.8%.
The map rates the ground, not the air in any home.
Local help
Gregory County, Local resources
Radon testing and mitigation in Gregory 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
Gregory County, Questions
Questions about radon in Gregory County
Are radon levels high in Gregory County?
Over the 2008 to 2017 laboratory totals, 66.7% of the radon tests reported to CDC for Gregory County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.3 pCi/L. Boyd County, NE, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 63.0% of its tests at or above 4 pCi/L.
Which counties border Gregory County?
Gregory County borders 5 counties: Tripp County, SD, Keya Paha County, NE, Charles Mix County, SD, Boyd County, NE and Lyman County, SD.
Products
Gregory County, Products
Testing a home in Gregory County
No CDC figure names Gregory County; the nearest county with one, Brule County (37 miles away), reported 62.5% 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 2 a short-term kit (2 to 90 days) is the quick first check in Gregory County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Gregory County, Bordering counties
Counties bordering Gregory County
Calculated by Radon411- Radon levels in Lyman County, SDEPA zone 1
100.0%at or above 4 pCi/L
Median 20.0 pCi/L · 5 tests
- Radon levels in Charles Mix County, SDEPA zone 1
63.6%at or above 4 pCi/L
Median 6.1 pCi/L · 11 tests
- Radon levels in Boyd County, NEEPA zone 1
63.0%at or above 4 pCi/L
Median 5.3 pCi/L · 46 tests
- Radon levels in Tripp County, SDEPA zone 2
57.1%at or above 4 pCi/L
Median 4.2 pCi/L · 7 tests
- Radon levels in Keya Paha County, NEEPA zone 2
23.1%at or above 4 pCi/L
Median 2.7 pCi/L · 13 tests
Gregory County, Cities and towns
Cities and towns in Gregory County
The Census Bureau estimates 4,037 residents in Gregory County for July 1, 2025, 44 more than in 2020 (+1.1%). Spread over its land, that is 4.0 people to the square mile. Its largest town, Gregory, has 1,250 residents, 31.0% of the total. Together its 6 incorporated places hold 58.4% of those residents; the other 41.6% live outside any of them. Reported testing is thin here: 15 tests over 2008 to 2017, or 3.7 for every 1,000 residents (2025 estimate), where South Dakota as a whole comes to 6.7.
From Gregory to Herrick, CDC publishes no figure by town: each reads Gregory County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Gregory | 1,250 | +2.6% | 31.0% |
| Burke | 590 | −0.8% | 14.6% |
| Bonesteel | 257 | +0.8% | 6.4% |
| Fairfax | 100 | +3.1% | 2.5% |
| Dallas | 83 | −3.5% | 2.1% |
| Herrick | 77 | Level | 1.9% |
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).
Gregory County, Homes
Homes in Gregory County
Gregory County is a place of houses on their own lots: 83% of its 2,199 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 1960 (1979 for South Dakota), and 50% 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 | Gregory County | South Dakota |
|---|---|---|
| Housing units | 2,199 | 402,364 |
| Detached houses | 83% | 67% |
| In buildings of 5 or more | 7% | 16% |
| Mobile homes | 7% | 8% |
| Built before 1960 | 50% | 29% |
| Built since 2000 | 17% | 28% |
| Middle year built | 1960 | 1979 |
| Owner-occupied | 78% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.