Radon Pros in Illinois

About Radon in Illinois

Last updated: March 2026

Illinois has a well-documented radon problem concentrated in the northern and central regions of the state. According to EPA mapping, most of the Chicago metropolitan area and surrounding collar counties are Zone 1 — the highest risk classification. Cook, DuPage, Lake, Will, Kane, and McHenry counties all have elevated average indoor radon levels driven by glacial soil deposits and limestone bedrock. Illinois was one of the first states to establish mandatory licensing for radon professionals, reflecting the severity of its radon problem. The Illinois Emergency Management Agency (IEMA) requires all radon mitigators and testers to pass state examinations and maintain active licenses. In real estate transactions, Illinois requires sellers to disclose known radon hazards under state law. Testing is not mandated but is standard practice in Chicagoland transactions — most buyers' agents in the collar counties treat it as essential due diligence. Illinois is distinctive because of the concentration of radon risk in its most densely populated region. While southern Illinois has lower average levels, the northern two-thirds of the state where the vast majority of the population lives is solidly Zone 1. The EPA recommends all Illinois homes north of I-70 be tested regardless of age or construction type.