Last reviewed October 16, 2026Sources
Every data set and guide this site cites, grouped by type, with the date we last retrieved it. State and county pages list their own state-specific sources at the bottom of each page.
| Group | Source | Retrieved |
|---|
| A. National radon data | EPA Map of Radon Zones (1993), text version and spreadsheet | October 16, 2026 |
| A. National radon data | EPA, EPA's Map of Radon Zones: National Summary | October 16, 2026 |
| A. National radon data | EPA, A Citizen's Guide to Radon (2016) | October 16, 2026 |
| A. National radon data | EPA, Consumer's Guide to Radon Reduction (2010 edition, archived) | October 16, 2026 |
| A. National radon data | EPA, Consumer's Guide to Radon Reduction (2016) | October 16, 2026 |
| A. National radon data | Census Bureau, 2020 ZCTA5-to-county relationship file | October 16, 2026 |
| B. State radon programs | PA DEP, Radon Test Results September 1986 to Current (data.pa.gov), retrieved Oct 16, 2026 | October 16, 2026 |
| B. State radon programs | 25 Pa. Code Chapter 240, radon certification | October 16, 2026 |
| B. State radon programs | Ohio Department of Health, Radon Data (county dashboard), retrieved Oct 16, 2026 | October 16, 2026 |
| B. State radon programs | Ohio Administrative Code 3701-69-04 | October 16, 2026 |
| C. Cost figures | HomeGuide, Radon Mitigation Cost (Feb 5, 2026) | October 16, 2026 |
Primary sources come first: EPA, state radon programs and the Census Bureau. A commercial cost survey (HomeGuide) is cited as plain text, only where no agency publishes current installed prices. See the methodology.