WilCo Soil-Type Risk Checker

In Williamson County, the ground under your house — not the city name — sets how much your foundation moves. Enter your ZIP for a quick read.

Why soil decides everything here

East of I-35 — Hutto, Taylor, Pflugerville — the county sits on deep Blackland Prairie clay, which swells when wet and shrinks hard in a drought. That seasonal movement is what walks a slab and cracks it. West toward Cedar Park and Leander, the ground turns to Edwards limestone, which barely moves. Same county, very different foundation risk. There’s a deeper explainer on why east-county homes crack more, and if you’re already seeing issues, the 7 warning signs help you read them.

Williamson County ZIP codes by soil type

The same table the checker above draws from, in full. Find your ZIP, then read what that zone actually means below.

What each zone means for your house

Higher risk — deep Blackland clay (east of I-35)

Houston Black clay has a high plasticity index, which is the technical way of saying it swells a lot when wet and shrinks hard when dry. Under a slab that movement is uneven — more at the exposed edges, less under the protected centre — so the slab flexes. Hutto, Taylor and the fast-growing flatlands around the Samsung plant sit squarely on it. Seasonal cracks and doors that stick by August are common here and often correct partway after the rains. Consistent moisture and good drainage genuinely help; a pattern of damage is worth an engineer’s look.

Moderate — the transition zone (Round Rock, Georgetown)

This is the messiest zone to generalise about, because the clay-to-rock boundary runs straight through it. Two houses a few streets apart can behave differently, and newer subdivisions add engineered fill on top of whatever was there. Sun City and Wolf Ranch in Georgetown, and Teravista and Forest Creek in Round Rock, all sit in this band. Movement happens but is usually milder than east county. An elevation survey is what tells you which situation your specific lot is in.

Lower — nearer the Edwards limestone (west county)

Along the Balcones Escarpment the ground turns rocky and barely moves. Cedar Park, Leander and Liberty Hill sit here. Foundation problems in west county are more often about lot grading, drainage, or poorly compacted fill than deep soil swelling — and piers can be shallower because stable rock is closer, which sometimes makes repair cheaper. If you’re seeing movement on limestone, water is the first thing a good crew should check.

Common questions

Does my ZIP code decide whether my foundation will crack?

No — it sets the odds, not the outcome. Drainage, the age of the house, how the lot was graded, under-slab plumbing leaks and tree placement all matter. Plenty of Hutto homes on the worst clay never have a problem because the water is managed well.

My street is on the boundary. What then?

Assume the more active soil until an elevation survey says otherwise. The transition isn’t a clean line on the ground, and cut-and-fill grading can put clay fill on a limestone lot.

Does the soil change what repair costs?

It changes pier depth, which is one of the two biggest cost drivers. Piers have to reach stable soil — shallow over the Austin Chalk, much deeper through east-county clay. See the cost ranges for what that does to a quote.

Foundation repair by city

Local detail on soil, neighborhoods and permits: Round Rock, Georgetown, Cedar Park, Leander, Hutto, Pflugerville and Taylor. Whatever your soil, the crack checker can tell you whether what you’re seeing is worth acting on, and the watering advisor covers keeping moisture steady without breaking your provider’s restrictions.