Is Gregory County, SD a radon risk area?

EPA places Gregory County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Gregory County sits at the 35th percentile nationally for radon potential — above 35 of every 100 rated counties.

How Gregory County compares

About 4,110 people live in Gregory County, South Dakota, spread over 1,014.95 square miles. That works out to roughly 4 people per square mile. Rank 956 by population within its EPA zone puts Gregory County at the 7th percentile among zone peers. Geologically, Gregory County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

EPA's Zone 2 rating for Gregory County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. Nothing about a Zone 2 label lowers the case for testing in Gregory County — EPA recommends it in every zone, moderate included.

Next steps for a home in Gregory County

Nothing about Gregory County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find South Dakota's state radon program

Gregory County's test kit answers today; a Airthings radon monitor keeps answering for Gregory 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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.