The Florida Department of Business and Professional Regulation developed Radon Protection Maps that are presented by the Florida Department of Health Radon Program website.
The counties mapped have areas where the addition of radon resistant construction features are recommended to prevent radon problems (more than 5% of new homes are expected to have annual average radon levels above the U.S. Environmental Protection Agency's action level in the identified areas). Counties not listed are those where fewer than 5% of new homes are expected to have elevated radon levels, so additional radon resistant construction techniques may not be needed to prevent radon problems. Note that currently these standards are voluntary. It would take a majority of the building permit issuing agencies in any county to adopt them for the standards to become a require code within that county. Only those counties that have areas where added radon resistant features are recommended have maps.
Radon Protection Maps by County maps describe the areas of the state where added radon resistant measures beyond the current energy efficient building code are needed to prevent indoor radon problems. The maps indicate where controls are generally unnecessary, or where passive or active control systems are recommended.
The maps represent the radon potential for buildings constructed on native soil with minimal disturbance of the ground. Radon source potential is defined as the average rate at which radon would enter a reference house that is modeled on specific soil profiles. However, during construction there is a great deal of digging that may unearth higher radium soil. Fill brought in during construction may also introduce higher radium into a building site.
The Department notes that the only way to know if a building has a radon problem is to test after completion.
See the maps at https://www.floridahealth.gov/environmental-health/radon/maps/protection-maps.html
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