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Radon Levels in Cass County, North Dakota

EPA puts Cass County in Zone 1, its highest radon zone, and high results are common there: 57.5% of the 862 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    57.5%

    1.8 pts below ND

    Cass
    57.5%
    ND
    59.3%

    862 tests, 2008 to 2017

  • Median result

    4.7pCi/L

    Action level reached

    Cass
    4.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    862

    2nd of 29 by tests

    Cass
    862
    Burleigh
    1,558

    Reported to CDC before any fix, 2008 to 2017

  • 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 ND

    20 of 29

    Middle half

    Cass
    57.5%
    Pembina
    82.5%

    By share, of 29 with 30+ tests

Read a result for Cass County

Starts at Cass County's median, 4.7 pCi/L

4.7pCi/L

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

EPA’s reading of 4.7 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. Cass County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Cass County, At a glance

Cass County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Cass 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Cass County, 2008 to 2017, laboratory

Reported results by concentration band, Cass County, 2008 to 2017, laboratory
Under 2 pCi/L: 21%2 to 4 pCi/L: 22%4 pCi/L and above: 57%

Of 862 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Cass County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L17920.8%
2 to 4 pCi/L18721.7%
4 pCi/L and above49657.5%
What these figures count

These are the 862 tests reported to CDC for Cass 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).

How to read these figures

Cass County, Compared

Cass County radon figures, compared

Calculated by Radon411

More than half: 57.5% of the 862 radon tests reported to CDC for Cass County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 20th of 29 North Dakota counties with 30 or more tests for the same period. That is 1.8 points below the 59.3% pooled from 53 North Dakota counties.

The median result, 4.7 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 105.6 pCi/L. The rest split 20.8% under 2 pCi/L and 21.7% from 2 to 4 (North Dakota: 18.3% and 22.4%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 57.5% share point the same way here.

4 of its 6 bordering counties with figures ran higher, led by Barnes County at 67.5%; Richland County reported 43.0%. Statewide for the same period, Pembina County reported the highest share (82.5%) and Williams County the lowest (33.8%).

CDC's ten-year totals for Cass County went from 614 tests (2005 to 2014) to 862 (2008 to 2017), the share going from 52.9% to 57.5%.

Nationally, every county with a figure for the same period pools to 35.7%; Cass County sits 21.8 points above it. CDC also counts 116 tests taken after mitigation in Cass County for the same period: tests in homes where a fix was already in.

Cass County against North Dakota, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Cass County
Cass County86257.5%4.7 pCi/LThis county
North Dakota, pooled53 counties, pooled6,60759.3%Not pooled+1.8 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−21.8 points
Pembina Countyhighest in the state5782.5%9.3 pCi/L+25.0 points
Williams Countylowest in the state20433.8%2.9 pCi/L−23.7 points
Barnes County, NDborders it8367.5%5.6 pCi/L+10.0 points
Ransom County, NDborders it15161.6%5.8 pCi/L+4.1 points
Clay County, MNborders it46561.5%5.6 pCi/L+4.0 points
Norman County, MNborders it15458.4%4.8 pCi/L+0.9 points
Traill County, NDborders it3751.4%4.1 pCi/L−6.1 points
Richland County, NDborders it9343.0%3.6 pCi/L−14.5 points
Steele County, NDborders it10.0%2.0 pCi/L−57.5 points
Where Cass County's reported results fell, 2008 to 2017, laboratory, beside North Dakota and the United States
ResultCass County testsCass County shareNorth Dakota shareU.S. shareAgainst North Dakota
Under 2 pCi/L17920.8%18.3%39.6%+2.5 points
2 to 4 pCi/L18721.7%22.4%24.7%−0.7 points
4 pCi/L and above49657.5%59.3%35.7%−1.8 points
Cass County ranked among the 29 North Dakota counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Mercer County15 of 298563.5%5.7 pCi/L
McLean County16 of 299563.2%5.6 pCi/L
Stark County17 of 2938662.4%5.1 pCi/L
Ransom County18 of 2915161.6%5.8 pCi/L
Foster County19 of 293161.3%4.5 pCi/L
Cass County20 of 2986257.5%4.7 pCi/L
McKenzie County21 of 294156.1%4.8 pCi/L
Morton County22 of 2926853.4%4.2 pCi/L
Traill County23 of 293751.4%4.1 pCi/L
Burleigh County24 of 291,55851.1%4.0 pCi/L
Pierce County25 of 293948.7%3.8 pCi/L
Cass County ten-year laboratory totals, against North Dakota's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestNorth Dakota, pooledChange from the row before
2008 to 201786257.5%4.7 pCi/L105.6 pCi/L59.3%−0.8 points
2007 to 201681658.3%4.8 pCi/L105.6 pCi/L58.7%+2.6 points
2006 to 201572755.7%4.5 pCi/L63.6 pCi/L56.3%+2.8 points
2005 to 201461452.9%4.3 pCi/L63.6 pCi/L54.0%First on file

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

Cass County, Geology

The ground under Cass County

Predicted

USGS's geologic map puts all of Cass County's mapped land in one class: high radon potential. The map puts 75.0% of Cass County in the area it calls Glacial Lakes and 24.9% in Great Plains (Glaciated). USGS gives the first a radon index of 14 and the second 13, both in the high band (12 to 17).

USGS's geologic areas under Cass County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Glacial LakesSilt and clay deposits of Glacial Lake Agassiz derived from Cretaceous shales containing higher than average amounts of uranium.High1475.0%
Great Plains (Glaciated)Glacial deposits derived from Cretaceous shales containing higher than average amounts of uranium.High1324.9%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Cass County beside the ground around it

On high-potential ground Cass County is close to North Dakota as a whole: 100% of its land against 98.9%. Of the 7 counties that border it, none has as large a share of high-potential ground; Barnes County comes nearest at 100%.

Share of land by USGS radon potential: Cass County, the 7 counties bordering it and North Dakota
AreaEPA zoneLow potentialModerate potentialHigh potential
Cass CountyZone 1NoneNone100%
Traill CountyZone 1NoneNone100%
Clay County, MNZone 1NoneNone100%
Ransom CountyZone 1NoneNone100%
Barnes CountyZone 1NoneNone100%
Steele CountyZone 1NoneNone100%
Norman County, MNZone 1NoneNone100%
Richland CountyZone 1NoneNone100%
North Dakota53 counties, pooled by land areaVariesNone1.1%98.9%

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

Local help

Cass County, Local resources

Radon testing and mitigation in Cass County

Listed radon businesses with an address in Cass County:

Listed radon professionals by town: Fargo, West Fargo, Horace

What North Dakota's program says
Phone
701-328-5166
Email
jOtto@nd.gov

What it means

Cass County, Questions

Questions about radon in Cass County

Are radon levels high in Cass County?

Over the 2008 to 2017 laboratory totals, 57.5% of the radon tests reported to CDC for Cass County, North Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.7 pCi/L. Of 29 North Dakota counties with 30 or more tests for the same period, 19 reported a higher share; pooled, the state comes to 59.3%.

Which counties border Cass County?

Cass County borders 7 counties: Traill County, ND, Clay County, MN, Ransom County, ND, Barnes County, ND, Steele County, ND, Norman County, MN and Richland County, ND.

Products

Cass County, Products

Testing a home in Cass County

In Cass County, 57.5% of 862 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 59.3% pooled across North Dakota. In Zone 1 the year-round level in Cass 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

Cass County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Cass County

Explore

Cass County, Bordering counties

Counties bordering Cass County

Calculated by Radon411

Cass County, Cities and towns

Cities and towns in Cass County

Cass County is growing: the Census Bureau puts it at 201,794 residents on July 1, 2025, up 9.1% from 184,897 in 2020. That works out to 114 people per square mile of land. Fargo alone is home to 136,275 of them, 67.5% of the total. Reported testing is thin here: 862 tests over 2008 to 2017, or 4.3 for every 1,000 residents (2025 estimate), where North Dakota as a whole comes to 8.3.

From Fargo to Ayr, CDC publishes no figure by town: each reads Cass County's.

The 12 largest cities and towns in Cass County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Fargo136,275+8.2%67.5%
West Fargo41,175+5.9%20.4%
Horace7,001+115.5%3.5%
Casselton2,485+0.3%1.2%
Mapleton1,496+12.3%0.7%
Kindred1,044+12.1%0.5%
Reile's Acres880+21.5%0.4%
Enderlinextends beyond Cass County860−2.4%Counted whole
Harwood845+6.2%0.4%
Argusville474−2.3%0.2%
Oxbow371−1.6%0.2%
Arthur328+0.6%0.2%
  • Hunter
  • Tower City (part)
  • Davenport
  • Leonard
  • Frontier
  • Grandin (part)
  • Buffalo
  • Page
  • Gardner
  • Amenia
  • North River
  • Prairie Rose
  • Briarwood
  • Alice
  • Ayr

27 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Cass County is counted whole, so it has no share.

Cass County, Homes

Homes in Cass County

Cass County has 87,497 homes, and many share a building: 40% are in buildings of five or more, 43% are detached houses, against 57% across North Dakota. Much of Cass County is recent building: 40% of its homes have gone up since 2000 and the middle year built is 1993, against 1981 for North Dakota. 52% of occupied homes are lived in by their owner (North Dakota: 63%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Cass County, North Dakota, 2019 to 2023
HomesCass CountyNorth Dakota
Housing units87,497374,866
Detached houses43%57%
In buildings of 5 or more40%25%
Mobile homes2%7%
Built before 196016%24%
Built since 200040%31%
Middle year built19931981
Owner-occupied52%63%

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