Johnson County, IA radon potential

EPA places Johnson County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Rank it against the rest of the country and Johnson County lands in the 96th percentile for radon potential.

How Johnson County compares

Johnson County, Iowa is home to about 160,080 people across 612.997 square miles. That works out to roughly 261 people per square mile. Within its own EPA zone, Johnson County is bigger by population than 88% of the counties that share it. Geologically, Johnson County is grouped into EPA Region 7 alongside 411 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Johnson County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. Some Johnson County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Testing and mitigation in Johnson County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Iowa's state radon program

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

Where Johnson County's figures come from

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