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

EPA's own radon map rates McDonough County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and McDonough County lands in the 84th percentile for radon potential.

McDonough County by the numbers

McDonough County, Illinois is home to about 26,662 people across 589.305 square miles. Population density there runs about 45 people per square mile. By population, McDonough County is the 498th largest of every county sharing its EPA zone — the 53rd percentile by population within that zone. EPA's geology-based Region 5 groups McDonough County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in McDonough County

McDonough 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. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in McDonough County specifically.

If McDonough County tests above the action level

For a McDonough 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 McDonough County, an ongoing number beats a one-time test - a Airthings radon monitor tracks McDonough 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 McDonough 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. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.