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Radon Levels in Marshall County, Minnesota

EPA puts Marshall County in Zone 1, its highest radon zone, and only 11 radon tests from it are on file with CDC (2023). Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Share at 4+ pCi/L

    56.4%

    12.3 pts above MN

    Marshall
    56.4%
    Minnesota
    44.1%

    101 tests, 2007 to 2016

  • Median result

    5.9pCi/L

    Action level reached

    Marshall
    5.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2007 to 2016

  • Tests reported

    101

    79th of 86 by tests

    Marshall
    101
    Hennepin
    32,628

    Reported to CDC before any fix, 2007 to 2016

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Minnesota

    41 of 86

    Middle half

    Marshall
    56.4%
    Rock
    84.6%

    By share, of 86 with 30+ tests

Read a result for Marshall County

Starts at Marshall County's median, 5.9 pCi/L

5.9pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 5.9 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Marshall County's median reported result, 2007 to 2016.

Interpret this readingWhat a fix costs

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 and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 67% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Marshall County, 2023

Share of reported tests at or above 4 pCi/L, by year, Marshall County
Share of reported tests at or above 4 pCi/L, by year, Marshall County
YearShare of reported tests at or above 4 pCi/L
201453.1%
201554.9%
201626.7%
201756.3%
201839.3%
201950.0%
202038.9%
202114.3%
202251.7%
20239.1%

2023: 9.1%. Across these years the share ran from 9.1% to 56.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 11 tests were reported to CDC for Marshall County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Marshall County, Compared

Marshall County radon figures, compared

Calculated by Radon411

More than half: 56.4% of the 101 radon tests reported to CDC for Marshall County over the 2007 to 2016 laboratory totals read at least 4 pCi/L. That places it 41st of 86 Minnesota counties with 30 or more tests for the same period. That is 12.3 points above the 44.1% pooled from 87 Minnesota counties.

The newest figure, in 2023, counts only 11 tests (9.1% at or above 4 pCi/L), too few to compare, so this reading uses the 101-test figure.

The median result, 5.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 46.4 pCi/L. The rest split 23.8% under 2 pCi/L and 19.8% from 2 to 4 (Minnesota: 26.9% and 29.0%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 56.4% share point the same way here.

4 of its 8 bordering counties with figures ran higher, led by Pembina County, ND at 82.8%; Roseau County reported 23.9%. Statewide for the same period, Rock County reported the highest share (84.6%) and Anoka County the lowest (17.1%).

The busiest year on file was 2015, with 51 tests reported; the quietest, 2019, had 8.

Nationally, every county with a figure for the same period pools to 35.8%; Marshall County sits 20.6 points above it. CDC also counts 6 tests taken after mitigation in Marshall County for the same period: tests in homes where a fix was already in.

Marshall County against Minnesota, the United States and nearby counties, 2007 to 2016, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Marshall County
Marshall County10156.4%5.9 pCi/LThis county
Minnesota, pooled87 counties, pooled120,76444.1%Not pooled−12.3 points
United States, pooled2,666 counties, pooled1,939,02535.8%Not pooled−20.6 points
Rock Countyhighest in the state20884.6%8.1 pCi/L+28.2 points
Anoka Countylowest in the state5,26517.1%1.9 pCi/L−39.3 points
Pembina County, NDborders it5882.8%8.9 pCi/L+26.4 points
Walsh County, NDborders it15377.8%9.5 pCi/L+21.4 points
Grand Forks County, NDborders it64575.7%8.7 pCi/L+19.3 points
Polk County, MNborders it34169.8%6.7 pCi/L+13.4 points
Pennington County, MNborders it14247.2%3.3 pCi/L−9.2 points
Beltrami County, MNborders it40238.3%3.2 pCi/L−18.1 points
Kittson County, MNborders it3333.3%2.5 pCi/L−23.1 points
Roseau County, MNborders it4623.9%2.1 pCi/L−32.5 points
Where Marshall County's reported results fell, 2007 to 2016, laboratory, beside Minnesota and the United States
ResultMarshall County testsMarshall County shareMinnesota shareU.S. shareAgainst Minnesota
Under 2 pCi/L2423.8%26.9%39.6%−3.1 points
2 to 4 pCi/L2019.8%29.0%24.6%−9.2 points
4 pCi/L and above5756.4%44.1%35.8%+12.3 points
Marshall County ranked among the 86 Minnesota counties with 30 or more tests, by share at or above 4 pCi/L, 2007 to 2016, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Clay County36 of 8638660.6%5.3 pCi/L
Rice County37 of 862,24960.5%4.9 pCi/L
Traverse County38 of 867259.7%4.8 pCi/L
Houston County39 of 861,06758.2%4.9 pCi/L
Goodhue County40 of 861,06657.5%4.7 pCi/L
Marshall County41 of 8610156.4%5.9 pCi/L
Otter Tail County42 of 8654656.4%4.6 pCi/L
Meeker County43 of 8673056.3%4.4 pCi/L
Norman County44 of 8614355.9%4.5 pCi/L
Olmsted County45 of 862,33355.5%4.5 pCi/L
Clearwater County46 of 867652.6%4.2 pCi/L
Marshall County radon tests by year, against Minnesota's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMinnesota, pooledChange from the row before
2023119.1%2.2 pCi/L13.0 pCi/L34.6%−42.6 points
20222951.7%4.4 pCi/L25.4 pCi/L31.6%+37.4 points
20211414.3%2.7 pCi/L14.6 pCi/L33.1%−24.6 points
20201838.9%3.3 pCi/L11.1 pCi/L31.8%−11.1 points
2019850.0%3.3 pCi/L53.5 pCi/L36.1%+10.7 points
20182839.3%3.1 pCi/L26.9 pCi/L38.3%−17.0 points
20171656.3%4.3 pCi/L9.4 pCi/L38.2%+29.6 points
20161526.7%2.7 pCi/L24.1 pCi/L37.0%−28.2 points
20155154.9%4.6 pCi/L33.6 pCi/L43.6%+1.8 points
20143253.1%5.3 pCi/L40.5 pCi/L42.9%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Marshall County, State data

Minnesota's own radon test data

Measured

What Minnesota's own agencies publish about radon tests in Marshall County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What the Minnesota Department of Health reports for Marshall County

Radon Testing (MN Public Health Data Access Portal): home radon tests reported voluntarily by private laboratories and licensed radon measurement professionals, counted by property. Period: 2016-2025.

Share with one or more tests at or above 4 pCi/L

46.3%

57 properties tested with one or more tests at or above 4 pCi/L

Median result

3.8 pCi/L

Average result

5.9 pCi/L

Tests behind these figures

12 properties tested a year on average

  • MDH says these data do not include all of the radon tests conducted in Minnesota.
  • Post-mitigation tests are excluded from the averages and the median; the percentages use each property's highest test.
  • Each home is unique and can have very different results than a neighbor's home; the only way to know is to test.
  • These figures describe tests reported to the Minnesota Department of Health in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.

Measured: Minnesota Department of Health data, 2016-2025.

Marshall County, Geology

The ground under Marshall County

Predicted

USGS's geologic map splits Marshall County: 67.3% of its land is high radon potential and 32.7% moderate. The map puts 67.2% of Marshall County in the area it calls Lake Agassiz Plain and 32.7% in Lake Agassiz Plain/Central Lowland-Western Lake Section. USGS gives the first a radon index of 15, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Marshall County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Lake Agassiz PlainSilt and clay deposits of Glacial Lake Agassiz derived from Cretaceous shales containing higher than average amounts of uranium.High1567.2%
Lake Agassiz Plain/Central Lowland-Western Lake SectionSilty and clayey glacial deposits and lake deposits.Moderate1032.7%

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

On high-potential ground Marshall County is close to Minnesota as a whole: 67.3% of its land against 61.1%. Of the 8 counties that border it, 5 have more high-potential ground, Grand Forks County, ND the most at 100%.

Share of land by USGS radon potential: Marshall County, the 8 counties bordering it and Minnesota
AreaEPA zoneLow potentialModerate potentialHigh potential
Marshall CountyZone 1None32.7%67.3%
Pennington CountyZone 1None70.5%29.5%
Polk CountyZone 1None3.5%96.5%
Kittson CountyZone 1None10.8%89.1%
Roseau CountyZone 1None75.4%24.5%
Grand Forks County, NDZone 1NoneNone100%
Walsh County, NDZone 1NoneNone100%
Pembina County, NDZone 1NoneNone99.8%
Beltrami CountyZone 2None94.7%5.3%
Minnesota87 counties, pooled by land areaVariesNone38.9%61.1%

The map rates the ground, not the air in any home.

Local help

Marshall County, Local resources

Radon testing and mitigation in Marshall County

What Minnesota's program says
Phone
651-201-4601
Email
health.indoorair@state.mn.us
Licensing of radon professionals
The Radon Licensing Act requires anyone who performs a radon test or radon mitigation, in a building they do not own or lease, must be licensed by MDH.
Disclosure when a home is sold or rented
The Minnesota Radon Awareness Act requires specific disclosure and education be provided to potential home buyers during residential real estate transactions in Minnesota.

What it means

Marshall County, Questions

Questions about radon in Marshall County

Are radon levels high in Marshall County?

In 2023, 9.1% of the radon tests reported to CDC for Marshall County, Minnesota were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.2 pCi/L. Of 86 Minnesota counties with 30 or more tests for the same period, 40 reported a higher share; pooled, the state comes to 44.1%.

Which counties border Marshall County?

Marshall County borders 8 counties: Pennington County, MN, Polk County, MN, Kittson County, MN, Roseau County, MN, Grand Forks County, ND, Walsh County, ND, Pembina County, ND and Beltrami County, MN.

Products

Marshall County, Products

Testing a home in Marshall County

In Marshall County, 56.4% of 101 tests reported to CDC over the 2007 to 2016 laboratory totals reached 4 pCi/L, against 44.1% pooled across Minnesota. 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

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

Marshall County, Cities and towns

Cities and towns in Marshall County

About 8,798 people live in Marshall County by the Census Bureau's estimate for July 1, 2025, 227 fewer than in 2020 (−2.5%). Spread over its land, that is 5.0 people to the square mile. No town dominates: Warren, the largest, has 1,558 residents, 17.7% of the total. Together its 11 incorporated places hold 49.4% of those residents; the other 50.6% live outside any of them. Reported testing is thin here: 101 tests over 2007 to 2016, or 11.5 for every 1,000 residents (2025 estimate), where Minnesota as a whole comes to 20.7.

From Warren to Strandquist, CDC publishes no figure by town: each reads Marshall County's.

The cities and towns in Marshall County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Warren1,558−2.7%17.7%
Stephen581−1.7%6.6%
Argyle531−1.8%6.0%
Alvarado390−1.8%4.4%
Newfolden345−2.3%3.9%
Middle River296−2.6%3.4%
Oslo239−0.4%2.7%
Grygla171−1.7%1.9%
Holt87−2.2%1.0%
Viking79−2.5%0.9%
Strandquist68−2.9%0.8%

11 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: 79% of its 4,416 homes are detached single-family houses, against 66% across Minnesota. Half of its homes were built before 1971, close to Minnesota's 1978: 39% date from before 1960 and 13% from 2000 or later. Owners live in 85% of the occupied homes (Minnesota: 72%), so for most households a test and a fix are their own to order.

Homes in Marshall County, Minnesota, 2019 to 2023
HomesMarshall CountyMinnesota
Housing units4,4162,519,538
Detached houses79%66%
In buildings of 5 or more6%19%
Mobile homes11%3%
Built before 196039%29%
Built since 200013%22%
Middle year built19711978
Owner-occupied85%72%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.