Radon levels in Williamson County, Texas
LowEPA Zone 3Predicted long-term basement average of 1.6 pCi/L (model estimate) across 17 ZIP codes - close to the US average of 1.8, close to the Texas average of 1.5. Ranked #141 of 253 Texas counties.
Test Williamson County, TX once anyway - radon varies house to house
The predicted basement average here is 1.6 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
We may earn a commission from Amazon at no extra cost to you.
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
1.6 ± 0.06
pCi/L predicted basement mean (model SD)
0.9 ± 0.06
pCi/L predicted upstairs (above-ground) mean
1.5-2.0
range of ZIP-level basement predictions in the county
What this means for Williamson
The typical Williamson County home is predicted below 2 pCi/L, the lowest band. That is the best case an area can show - but it describes the average house, and the ZIP-level predictions within the county still span 1.5 to 2.0 pCi/L.
The 1993 EPA zone (3) and the 2001-2021 model agree for Williamson. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable Texas counties: Wichita County (1.7), Kinney County (1.6), Camp County (1.6), Collin County (1.6). The state's highest is Hemphill County at 2.5 pCi/L.
ZIP codes in Williamson County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
| ZIP | Basement | Upstairs | Grade |
|---|---|---|---|
| 78613 | 1.6 ± 0.06 | 0.9 | Low |
| 78664 | 1.7 ± 0.06 | 1.0 | Low |
| 78681 | 1.6 ± 0.06 | 0.8 | Low |
| 78665 | 1.8 ± 0.05 | 1.0 | Low |
| 78729 | 1.5 ± 0.06 | 0.8 | Low |
| 78626 | 1.8 ± 0.06 | 1.0 | Low |
| 78628 | 1.7 ± 0.06 | 0.8 | Low |
| 78634 | 1.6 ± 0.06 | 0.7 | Low |
| 78717 | 1.5 ± 0.06 | 0.9 | Low |
| 78633 | 1.5 ± 0.06 | 0.8 | Low |
| 76574 | 1.6 ± 0.07 | 0.7 | Low |
| 78642 | 1.8 ± 0.06 | 0.9 | Low |
| 76527 | 1.9 ± 0.06 | 0.8 | Low |
| 76537 | 2.0 ± 0.06 | 0.9 | Low |
| 76530 | 1.7 ± 0.06 | 0.8 | Low |
| 76578 | 1.6 ± 0.06 | 0.8 | Low |
| 78615 | 1.6 ± 0.06 | 0.8 | Low |
If your test comes back at 4 pCi/L or higher
Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.
Williamson County radon questions
- Is radon high in Williamson County, Texas?
- Low. The model predicts a long-term basement average of 1.6 pCi/L in Williamson County (close to the US average of 1.8 and close to the Texas average of 1.5). That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Ranked 141 of 253 Texas counties.
- Should I test for radon in Williamson County?
- Yes, once. The EPA recommends testing every home regardless of area, and the model's ZIP-level predictions in Williamson County already range from 1.5 to 2.0 pCi/L. A short-term kit costs little and settles the question for your house.
- What does EPA Radon Zone 3 mean for Williamson County?
- Zone 3 - low potential (< 2 pCi/L). The zone map dates from 1993 and classifies whole counties. The 2001-2021 model agrees with the zone here. Neither replaces a test of your own home.
- How much does radon mitigation cost in Williamson County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Texas quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.
← All Texas counties · How to test · Radon in a home sale · Methodology