Is Boone County, IL a radon risk area?
EPA places Boone County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally that's the 90th percentile for radon potential — Boone County outranks 90% of every county EPA has rated.
How Boone County compares
About 53,313 people live in Boone County, Illinois, spread over 280.749 square miles. Population density there runs about 190 people per square mile. Rank 301 by population within its EPA zone puts Boone County at the 72nd percentile among zone peers. Geologically, Boone 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
Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Boone County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Boone County will test well under the action level, and EPA's guidance is to test regardless of zone.
If Boone County tests above the action level
Nothing about Boone County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.
Find Illinois's state radon program
Boone County's test kit answers today; a Airthings radon monitor keeps answering for Boone County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.
More on how this number was built
Boone County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.