Cass County, IL radon potential

EPA places Cass 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 Cass County lands in the 77th percentile for radon potential.

How Cass County compares

Cass County, Illinois is home to about 12,713 people across 375.754 square miles. That works out to roughly 34 people per square mile. Within its own EPA zone, Cass County is bigger by population than 34% of the counties that share it. EPA's geology-based Region 5 groups Cass County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Cass County

Where the national indoor average runs about 1.3 pCi/L, Cass County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. That doesn't mean every Cass 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 Cass County tests above the action level

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 Illinois's state radon program

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

Where Cass County's figures come from

Cass 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.