Adams County · EPA Radon Zone 1
Radon Testing & Mitigation in Thornton, Colorado
The largest city in Adams County by population, located approximately 10 miles north of downtown Denver.
Thornton at a glance
- Population
- 141,867 (2020)
- County
- Adams County
- Incorporated
- June 12, 1956
- Area
- 37.9 sq mi
- EPA Radon Zone
- Zone 1 (highest risk classification)
- School districts
- Adams 12 Five Star Schools · Mapleton Public Schools (Adams 14) · School District 27J
Population: U.S. Census Bureau 2020 Decennial Census.
Radon in Thornton
Thornton is located in Adams County, which the U.S. Environmental Protection Agency designates as Radon Zone 1 — the highest-risk classification, indicating predicted average indoor radon levels at or above the EPA action level of 4 pCi/L.
Thornton was the first fully planned community in Adams County. Founded as a postwar planned suburb, the city grew from 5,500 residents in 1955 to over 141,000 by 2020. The original 1950s-1970s housing stock — the bulk of the city's older neighborhoods — was built before radon-resistant new construction (RRNC) standards became common in the 1990s.
Statewide, 46.9% of pre-mitigation home radon tests in Colorado come back at or above the EPA action level (4 pCi/L), based on 214,362 tests in the CDPHE 2005–2024 statewide dataset. Whether you own or rent in Thornton, testing is the only way to know your home's level.
Radon costs in Thornton → What a mitigation install typically runs in Colorado, and the factors that move the price up or down.
Sources: U.S. EPA Map of Radon Zones; CDPHE Colorado Radon Tests 2005–2024; U.S. Census Bureau 2020 Decennial Census; city naming via Wikipedia.
Get a free quote for radon mitigation in Adams County.
We’re NRPP-certified and Colorado state-licensed. A standard sub-slab depressurization install reduces indoor radon by 95%+ in most Adams County homes — exact quote in 24 hours.
- 24-hour quote turnaround
- Installed in 4–6 hours
- Post-install re-test included
- Radon-mitigation listing feature
Or call us at (866) 398-9858 — same-day response during business hours.
Prefer the data first? Download the free Colorado Radon Risk Map.
Other Adams County cities
Same county, same EPA Radon Zone 1 classification.
See the full county dataset at Adams County radon levels.