What EPA's radon map says about Sheridan County

EPA places Sheridan 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. Sheridan County sits at the 66th percentile nationally for radon potential — above 66 of every 100 rated counties.

How Sheridan County compares

About 1,268 people live in Sheridan County, North Dakota, spread over 972.226 square miles. That works out to roughly 1 people per square mile. Among counties sharing Sheridan County's EPA zone, it outranks 1% of them by population. EPA's geology-based Region 8 groups Sheridan County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Sheridan County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Sheridan County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Sheridan County tests above the action level

Mitigation cost doesn't depend on Sheridan 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

Sheridan County's test kit answers today; a Airthings radon monitor keeps answering for Sheridan County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

Sheridan County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.