Radon levels in Colorado

About radon in Colorado

About half of Colorado homes have radon above the EPA's 4 pCi/L action level, according to the Colorado Department of Public Health and Environment, and radon is responsible for about 500 lung cancer deaths in the state each year (CDPHE; CDPHE).

Our Colorado figures come from CDPHE's county test data, released for public reuse: 237,408 tests recorded from 2005 to 2025. Across them, 46% were at or above 4 pCi/L, close to the state's own estimate. The data is newer than most states' and includes tests from the last few years.

High results are common almost everywhere in Colorado. In our data, Morgan County on the northeastern plains has the highest share of high tests (64%) and Bent County in the southeast the lowest (17%). Colorado's source does not report the share of results between 2 and 4 pCi/L or an average level, so its county pages show a little less detail than some other states.

Colorado has strengthened its radon rules in recent years. Radon testers and mitigators must now be licensed by the Department of Regulatory Agencies (DORA). Since August 2023, home sale contracts must include the seller's known radon tests, reports and mitigation, along with CDPHE's radon brochure, and landlords must give similar disclosures to tenants (SB23-206).

For households that cannot afford a mitigation system, CDPHE runs a Low-Income Radon Mitigation Assistance program (CDPHE). Pick your county below to see its results and how it compares with nearby counties.

Written and reviewed by Ray Roman · 2026-11-03