Johnson County, TX: EPA's radon zone, explained

EPA's own radon map rates Johnson County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. Nationally, Johnson County ranks higher in radon potential than 29% of rated counties (the 29th percentile).

Johnson County by the numbers

Johnson County, Texas is home to about 210,547 people across 725.062 square miles. That works out to roughly 290 people per square mile. By population, Johnson County is the 124th largest of every county sharing its EPA zone — the 88th percentile by population within that zone. EPA's geology-based Region 6 groups Johnson County with 502 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

A Zone 3 county like Johnson County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. A Zone 3 label describes Johnson County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Next steps for a home in Johnson County

For a Johnson County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Texas's state radon program

For Johnson County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Johnson County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Johnson County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Johnson County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.