Washington County, IL radon potential

EPA's own radon map rates Washington County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally, Washington County ranks higher in radon potential than 42% of rated counties (the 42nd percentile).

How Washington County compares

Washington County, Illinois is home to about 13,535 people across 562.597 square miles. Averaged across its land area, Washington County runs about 24 people per square mile. Within its own EPA zone, Washington County is bigger by population than 28% of the counties that share it. Geologically, Washington 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 Washington County

Washington County's Zone 2 prediction clears the 1.3 pCi/L national indoor average without reaching EPA's own 4 pCi/L point for recommending a fix. Middle-of-the-pack doesn't mean risk-free for any one Washington County address — a moderate county average still leaves individual homes to test either side of it.

If Washington County tests above the action level

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Illinois's state radon program

For Washington County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Washington 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 Washington County's figures come from

Washington 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.