Is St. Johns County, FL a radon risk area?

EPA's own radon map rates St. Johns County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. Rank it against the rest of the country and St. Johns County lands in the 30th percentile for radon potential.

How St. Johns County compares

About 334,928 people live in St. Johns County, Florida, spread over 600.663 square miles. Population density there runs about 558 people per square mile. Rank 81 by population within its EPA zone puts St. Johns County at the 92nd percentile among zone peers. Geologically, St. Johns County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

Zone vs. an actual test

Well clear of both the 1.3 pCi/L national indoor average and EPA's 4 pCi/L action level, St. Johns County's Zone 3 prediction is the low end of the scale. A Zone 3 label describes St. Johns County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Testing and mitigation in St. Johns County

Nothing about St. Johns County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Florida's state radon program

St. Johns County's test kit answers today; a Airthings radon monitor keeps answering for St. Johns County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.