Brown County, IL radon potential

Brown County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Brown County sits at the 72nd percentile nationally for radon potential — above 72 of every 100 rated counties.

Where Brown County sits nationally

Brown County, Illinois is home to about 6,307 people across 305.727 square miles. Averaged across its land area, Brown County runs about 21 people per square mile. Within its own EPA zone, Brown County is bigger by population than 18% of the counties that share it. Geologically, Brown County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Brown County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. That doesn't mean every Brown 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.

Testing and mitigation in Brown 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 Illinois's state radon program

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

Where Brown County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Brown County carries, the zone explainer covers what it does and doesn't tell you about any one house.