Greene County, IL radon potential

Greene County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Greene County in the 76th percentile nationally for radon potential — higher than 76% of the counties EPA has rated.

Greene County by the numbers

Greene County, Illinois is home to about 11,417 people across 543.144 square miles. Averaged across its land area, Greene County runs about 21 people per square mile. Within its own EPA zone, Greene County is bigger by population than 31% of the counties that share it. Geologically, Greene County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Zone vs. an actual test

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

Where Greene County's figures come from

Greene County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Greene County carries, the zone explainer covers what it does and doesn't tell you about any one house.