Free county-level expansive-soil (shrink-swell clay) risk data for 2,618 U.S. jurisdictions (2,545 counties, 64 Louisiana parishes, 9 independent cities) with sufficient USDA SSURGO coverage — ready for reporting, with the method below. Free to republish with attribution; no signup, no license fee.
National — all 2,618 counties ↓
Per-state files, ranked worst-first:
USDA's SSURGO soil survey measures linear extensibility (LEP) — how much a soil shrinks and swells with moisture. For each mapped soil component we take the maximum LEP of any horizon beginning within the top 100 cm; a component is classed highly expansive at LEP ≥ 6% (moderately at 3–6%). Component acreage is then area-weighted to the county, and we report the share of the county's mapped soil acreage that is highly expansive. Jurisdictions are ranked nationally and within their state and tiered (Severe ≥30% · High 15–<30% · Moderate 5–<15% · Low <5%). State averages are unweighted means of scored county percentages, across the 46 states with sufficient coverage. The "dominant clay series" column lists up to three expansive soil series ranked by estimated mapped acreage. Jurisdictions without sufficient SSURGO coverage are excluded rather than estimated.
County-scale exposure context from federal soil surveys. It is not a per-home reading: soil varies lot to lot, so a higher-risk county still holds lower-risk lots and vice versa. We ask that reporting keep that caveat — it's the honest read of the data.
Risk metrics are computed from USDA SSURGO soil survey data (linear extensibility of soil components, area-weighted by county). Soil varies lot to lot — this is county-scale context, not a substitute for a site-specific geotechnical or structural assessment.