What EPA's radon map says about Lake County

EPA's own radon map rates Lake County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Lake County lands in the 76th percentile for radon potential.

Where Lake County sits nationally

About 11,006 people live in Lake County, South Dakota, spread over 562.905 square miles. That works out to roughly 20 people per square mile. Among counties sharing Lake County's EPA zone, it outranks 30% of them by population. Lake County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Lake County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. Being in Zone 1 raises the odds Lake County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

If Lake County tests above the action level

Mitigation cost doesn't depend on Lake 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 South Dakota's state radon program

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

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Lake County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.