Williamson County, TX radon potential

Williamson County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Williamson County sits at the 32nd percentile nationally for radon potential — above 32 of every 100 rated counties.

Where Williamson County sits nationally

Williamson County, Texas is home to about 727,480 people across 1,115.869 square miles. Population density there runs about 652 people per square mile. Within its own EPA zone, Williamson County is bigger by population than 96% of the counties that share it. Geologically, Williamson County is grouped into EPA Region 6 alongside 502 other counties that share its rock and soil setting.

What this actually means for a house in Williamson County

Williamson County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. A Zone 3 rating means Williamson County's county-wide average is predicted low, but EPA is explicit that a meaningful share of homes in low-potential zones still test above the action level — a low zone is not a reason to skip testing.

Testing and mitigation in Williamson County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Texas's state radon program

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

Where Williamson County's figures come from

Williamson County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.