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

Massac County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Rank it against the rest of the country and Massac County lands in the 9th percentile for radon potential.

Where Massac County sits nationally

Massac County, Illinois is home to about 13,627 people across 237.152 square miles. Averaged across its land area, Massac County runs about 57 people per square mile. By population, Massac County is the 739th largest of every county sharing its EPA zone — the 28th percentile by population within that zone. EPA's geology-based Region 5 groups Massac County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Massac County

Massac County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. Don't read Zone 3 as a pass for Massac County — EPA's guidance to test every home makes no exception for counties predicted low.

If Massac County tests above the action level

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

Where Massac County's figures come from

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