Humboldt County, IA: EPA's radon zone, explained

EPA's own radon map rates Humboldt County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Humboldt County sits at the 75th percentile nationally for radon potential — above 75 of every 100 rated counties.

How Humboldt County compares

Humboldt County, Iowa is home to about 9,617 people across 434.372 square miles. Averaged across its land area, Humboldt County runs about 22 people per square mile. By population, Humboldt County is the 775th largest of every county sharing its EPA zone — the 27th percentile by population within that zone. Humboldt 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 Humboldt County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Humboldt County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Humboldt 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 Humboldt County tests above the action level

For a Humboldt County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Iowa's state radon program

For Humboldt County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Humboldt County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Humboldt County's figures come from

Humboldt County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.