Is Clark County, IL a radon risk area?

EPA places Clark County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 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 Clark County lands in the 43rd percentile for radon potential.

How Clark County compares

About 15,076 people live in Clark County, Illinois, spread over 501.39 square miles. That works out to roughly 30 people per square mile. Rank 715 by population within its EPA zone puts Clark County at the 31st percentile among zone peers. Geologically, Clark County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Zone vs. an actual test

Neither at the 4 pCi/L action level nor down at the roughly 1.3 pCi/L national indoor norm, Clark County's Zone 2 prediction lands in the gap between the two. A county-wide moderate average, like Clark County's, can still hide a specific house well above or below it — testing is what actually answers the question.

Testing and mitigation in Clark County

Nothing about Clark County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Illinois's state radon program

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

Clark 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.