Is Hamlin County, SD a radon risk area?

Hamlin County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Hamlin County ranks higher in radon potential than 72% of rated counties (the 72nd percentile).

Where Hamlin County sits nationally

About 6,596 people live in Hamlin County, South Dakota, spread over 507.071 square miles. That works out to roughly 13 people per square mile. Rank 862 by population within its EPA zone puts Hamlin County at the 19th percentile among zone peers. Geologically, Hamlin County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

What this actually means for a house in Hamlin County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Hamlin County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Hamlin County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

If Hamlin County tests above the action level

Nothing about Hamlin 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

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

Hamlin 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.