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

EPA places Monroe County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally that's the 52nd percentile for radon potential — Monroe County outranks 52% of every county EPA has rated.

How Monroe County compares

Monroe County, Illinois is home to about 34,969 people across 385.301 square miles. Averaged across its land area, Monroe County runs about 91 people per square mile. By population, Monroe County is the 441st largest of every county sharing its EPA zone — the 57th percentile by population within that zone. Geologically, Monroe 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

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Monroe County's Zone 2 prediction. A county-wide moderate average, like Monroe County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If Monroe County tests above the action level

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

Where Monroe County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Monroe County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.