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

Randolph County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Randolph County sits at the 50th percentile nationally for radon potential — above 50 of every 100 rated counties.

How Randolph County compares

Randolph County, Illinois is home to about 29,903 people across 575.367 square miles. Averaged across its land area, Randolph County runs about 52 people per square mile. By population, Randolph County is the 487th largest of every county sharing its EPA zone — the 53rd percentile by population within that zone. EPA's geology-based Region 5 groups Randolph County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

EPA's Zone 2 rating for Randolph County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. A Zone 2 rating is a moderate county-wide average, not a guarantee about any one house in Randolph County — testing is the only way to know an individual home's actual level.

If Randolph County tests above the action level

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

Where Randolph County's figures come from

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