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

EPA places Whiteside 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. Rank it against the rest of the country and Whiteside County lands in the 91st percentile for radon potential.

Where Whiteside County sits nationally

Whiteside County, Illinois is home to about 54,657 people across 684.099 square miles. That works out to roughly 80 people per square mile. By population, Whiteside County is the 294th largest of every county sharing its EPA zone — the 72nd percentile by population within that zone. EPA's geology-based Region 5 groups Whiteside County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Whiteside County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Whiteside County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Testing and mitigation in Whiteside County

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

Where Whiteside County's figures come from

Whiteside 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.