Henry County, IL: EPA's radon zone, explained
EPA's own radon map rates Henry County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Henry County ranks higher in radon potential than 90% of rated counties (the 90th percentile).
How Henry County compares
Henry County, Illinois is home to about 48,177 people across 823.186 square miles. Averaged across its land area, Henry County runs about 59 people per square mile. By population, Henry County is the 323rd largest of every county sharing its EPA zone — the 70th percentile by population within that zone. Geologically, Henry County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.
What this actually means for a house in Henry County
Henry 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. Being in Zone 1 raises the odds Henry County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.
Testing and mitigation in Henry County
For a Henry 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 Henry County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Henry County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.
Where Henry County's figures come from
The methodology guide shows exactly which EPA and Census sources feed Henry County's numbers. Whatever zone Henry County carries, the zone explainer covers what it does and doesn't tell you about any one house.