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 Marshall County, South Dakota
EPA puts Marshall County in Zone 1, its highest radon zone, and only 16 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
62.5%
Sargent County
- Sargent
- 62.5%
- Richland
- 35.1%
3 of 5 neighbours have 30+ tests, 2006 to 2015
Nearest county
59.6%
Brown County, 38 miles
- Brown
- 59.6%
- SD
- 58.8%
Share at 4+ pCi/L, 52 tests, 2006 to 2015
Ground above low
100.0%
1.0 pts above SD
- Marshall
- 100.0%
- SD
- 99.0%
Share of land USGS rates moderate or high potential
Tests reported
17
Too few for a share
- Marshall
- 17
- Needed
- 30
2007 to 2016, 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 Marshall 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
Marshall County, At a glance
Marshall County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Marshall 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 Marshall County, 2008 to 2017, laboratory
CDC holds 16 reported tests for Marshall County over the 2008 to 2017 laboratory totals, with a median of 10.5 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Marshall County beside the counties around it is how this page reads it.
What these figures count
Only 16 tests were reported to CDC for Marshall 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).
Marshall County, Compared
Marshall County radon figures, compared
Calculated by Radon411CDC's largest figure for Marshall County rests on 17 tests over the 2007 to 2016 laboratory totals, 14 of them at or above 4 pCi/L, so each test moves its share by 5.9 points and no rank or comparison is drawn from it. Results reached as high as 26.8 pCi/L, with a middle value of 11.7 pCi/L.
Of the counties bordering it, 3 have a figure over the 2006 to 2015 laboratory totals: Sargent County, ND reported the largest share at or above 4 pCi/L, 62.5%, and Richland County, ND the smallest, 35.1%, with Brown County at 59.6% between. Farther out, Grant County (57 miles away) at 64.6%, Codington County (57 miles away) at 65.3% and Edmunds County (82 miles away) at 61.8% 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 Marshall 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.
Marshall County, Geology
The ground under Marshall County
PredictedUSGS's geologic map puts all of Marshall County's mapped land in one class: high radon potential. The map puts 70.8% of Marshall County in the area it calls Missouri Coteau/James River Lowland/Coteau des Prairies and 29.2% in Glacial Lake Dakota. USGS gives both 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 | 70.8% |
| Glacial Lake Dakota | Silt and clay glacial lake deposits. | High | 14 | 29.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Marshall County beside the ground around it
Marshall 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; Richland County, ND comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Marshall County, Local resources
Radon testing and mitigation in Marshall 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
Marshall County, Questions
Questions about radon in Marshall County
Are radon levels high in Marshall County?
Over the 2008 to 2017 laboratory totals, 81.3% of the radon tests reported to CDC for Marshall County, South Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 10.5 pCi/L. Of the counties bordering it, 3 have a figure over the 2006 to 2015 laboratory totals: Sargent County, ND reported the largest share at or above 4 pCi/L, 62.5%, and Richland County, ND the smallest, 35.1%, with Brown County at 59.6% between.
Which counties border Marshall County?
Marshall County borders 5 counties: Day County, SD, Sargent County, ND, Roberts County, SD, Brown County, SD and Richland County, ND.
Products
Marshall County, Products
Testing a home in Marshall County
No CDC figure names Marshall County; the nearest county with one, Brown County (38 miles away), reported 59.6% 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 Marshall 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
EcoQube Flex battery digital radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Alarm
- Screen, app
Method: Ion chamber
First reading: Within 15 minutes
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Marshall County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Marshall County
Explore
Marshall County, Bordering counties
Counties bordering Marshall County
Calculated by Radon411- Radon levels in Sargent County, NDEPA zone 1
62.5%at or above 4 pCi/L
Median 4.8 pCi/L · 40 tests
- Radon levels in Brown County, SDEPA zone 1
59.6%at or above 4 pCi/L
Median 4.4 pCi/L · 52 tests
- Radon levels in Day County, SDEPA zone 1
50.0%at or above 4 pCi/L
Median 4.0 pCi/L · 6 tests
- Radon levels in Roberts County, SDEPA zone 1
42.1%at or above 4 pCi/L
Median 3.1 pCi/L · 19 tests
- Radon levels in Richland County, NDEPA zone 1
35.1%at or above 4 pCi/L
Median 3.0 pCi/L · 134 tests
Marshall County, Cities and towns
Cities and towns in Marshall County
The Census Bureau estimates 4,426 residents in Marshall County for July 1, 2025, 125 more than in 2020 (+2.9%). Spread over its land, that is 5.3 people to the square mile. Its largest town, Britton, has 1,199 residents, 27.1% of the total. Together its 5 incorporated places hold 43.4% of those residents; the other 56.6% live outside any of them. CDC's 17 reported tests for 2007 to 2016 work out to 3.8 per 1,000 residents (2025 estimate), close to South Dakota's 5.7.
From Britton to Lake City, CDC publishes no figure by town: each reads Marshall County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Britton | 1,199 | −0.6% | 27.1% |
| Veblen | 313 | −1.3% | 7.1% |
| Langford | 276 | −0.7% | 6.2% |
| Eden | 91 | −1.1% | 2.1% |
| Lake City | 44 | +2.3% | 1.0% |
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).
Marshall County, Homes
Homes in Marshall County
Marshall County is a place of houses on their own lots: 82% of its 2,430 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 1969 (1979 for South Dakota), and 41% date from before 1960. Owners live in 80% of the occupied homes (South Dakota: 69%), so for most households a test and a fix are their own to order.
| Homes | Marshall County | South Dakota |
|---|---|---|
| Housing units | 2,430 | 402,364 |
| Detached houses | 82% | 67% |
| In buildings of 5 or more | 6% | 16% |
| Mobile homes | 8% | 8% |
| Built before 1960 | 41% | 29% |
| Built since 2000 | 17% | 28% |
| Middle year built | 1969 | 1979 |
| Owner-occupied | 80% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.