What EPA's radon map says about Ransom County
EPA places Ransom County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Ransom County ranks higher in radon potential than 71% of rated counties (the 71st percentile).
How Ransom County compares
About 5,590 people live in Ransom County, North Dakota, spread over 862.472 square miles. Averaged across its land area, Ransom County runs about 6 people per square mile. Among counties sharing Ransom County's EPA zone, it outranks 15% of them by population. Ransom County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.
Zone vs. an actual test
Ransom County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Ransom County will test well under the action level, and EPA's guidance is to test regardless of zone.
Next steps for a home in Ransom County
Mitigation cost doesn't depend on Ransom County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.
Find North Dakota's state radon program
Ransom County's test kit answers today; a Airthings radon monitor keeps answering for Ransom County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.
More on how this number was built
The methodology guide shows exactly which EPA and Census sources feed Ransom County's numbers. Whatever zone Ransom County carries, the zone explainer covers what it does and doesn't tell you about any one house.