Alexander County, IL: EPA's radon zone, explained

Alexander County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. That puts Alexander County in the 3rd percentile nationally for radon potential — higher than 3% of the counties EPA has rated.

Alexander County by the numbers

Alexander County, Illinois is home to about 4,594 people across 235.394 square miles. Averaged across its land area, Alexander County runs about 20 people per square mile. By population, Alexander County is the 951st largest of every county sharing its EPA zone — the 8th percentile by population within that zone. EPA's geology-based Region 5 groups Alexander County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Alexander County

At Zone 3, Alexander County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. Don't read Zone 3 as a pass for Alexander County — EPA's guidance to test every home makes no exception for counties predicted low.

If Alexander County tests above the action level

For a Alexander 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 Illinois's state radon program

For Alexander County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Alexander 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 Alexander County's figures come from

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