What EPA's radon map says about Douglas County

Douglas County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally that's the 82nd percentile for radon potential — Douglas County outranks 82% of every county EPA has rated.

Douglas County by the numbers

About 19,824 people live in Douglas County, Illinois, spread over 416.65 square miles. Averaged across its land area, Douglas County runs about 48 people per square mile. Among counties sharing Douglas County's EPA zone, it outranks 46% of them by population. EPA's geology-based Region 5 groups Douglas County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Douglas County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Douglas County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Douglas County

Mitigation cost doesn't depend on Douglas County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Illinois's state radon program

Douglas County's test kit answers today; a Airthings radon monitor keeps answering for Douglas 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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Douglas County carries, the zone explainer covers what it does and doesn't tell you about any one house.