North Dakota: 53 counties covered
Of 53 rated North Dakota counties, 53 are in EPA's highest radon-potential zone (Zone 1) — but every county page links to testing guidance regardless of zone, because a county rating is a county-wide average, not a reading for any one house.
- Cass County
- Burleigh County
- Grand Forks County
- Ward County
- Williams County
- Morton County
- Stark County
- Stutsman County
- Richland County
- McKenzie County
- Rolette County
- Ramsey County
- Barnes County
- Walsh County
- McLean County
- Mountrail County
- Mercer County
- Traill County
- Pembina County
- Bottineau County
- Benson County
- Ransom County
- McHenry County
- Dickey County
- LaMoure County
- Dunn County
- Pierce County
- Wells County
- Sioux County
- Sargent County
- Cavalier County
- Foster County
- Emmons County
- Nelson County
- Bowman County
- McIntosh County
- Hettinger County
- Renville County
- Kidder County
- Eddy County
- Grant County
- Griggs County
- Burke County
- Adams County
- Divide County
- Towner County
- Oliver County
- Logan County
- Golden Valley County
- Steele County
- Sheridan County
- Billings County
- Slope County