What EPA's radon map says about Sioux County

Sioux County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Sioux County sits at the 87th percentile nationally for radon potential — above 87 of every 100 rated counties.

Where Sioux County sits nationally

About 36,554 people live in Sioux County, Iowa, spread over 767.911 square miles. Population density there runs about 48 people per square mile. Among counties sharing Sioux County's EPA zone, it outranks 61% of them by population. Sioux County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Sioux County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Sioux County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Being in Zone 1 raises the odds Sioux 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.

Testing and mitigation in Sioux County

Mitigation cost doesn't depend on Sioux 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 Iowa's state radon program

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

The methodology guide shows exactly which EPA and Census sources feed Sioux County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.