Ranking · states and counties
Where the US has the most clay soil
Louisiana and South Dakota have the highest share of clayey topsoil of any state (20.1% each of mapped land). County by county, Stanley County, SD leads, with clay at the surface on 85% of its land.
- Top state
- 20.1%
- Louisiana
- Top county
- 85%
- Stanley County, SD
- Clayey topsoil, US
- 4%
- share of all mapped land
States with the most clay topsoil
Share of mapped land
| State | Clayey topsoil | Loamy | Sandy |
|---|---|---|---|
| 1. Louisiana | 20.1% | 55% | 7% |
| 2. South Dakota | 20.1% | 75% | 4% |
| 3. Texas | 15.9% | 56% | 15% |
| 4. Hawaii | 13.8% | 59% | 7% |
| 5. Mississippi | 10.4% | 85% | 3% |
| 6. Arkansas | 8.7% | 80% | 3% |
| 7. Montana | 7.3% | 81% | <1% |
| 8. Kentucky | 4.0% | 85% | 1% |
| 9. North Dakota | 4.0% | 90% | 6% |
| 10. Alabama | 3.9% | 78% | 17% |
| 11. California | 3.9% | 57% | 21% |
| 12. Kansas | 3.9% | 89% | 6% |
| 13. Vermont | 3.8% | 82% | 8% |
| 14. Oklahoma | 3.4% | 79% | 10% |
| 15. Ohio | 2.9% | 88% | 1% |
The 25 counties with the most clay
Share of mapped land
| County | Clayey topsoil | Poorly drained | Most common soil |
|---|---|---|---|
| 1. Stanley County, SD | 85% | 1% | Sansarc |
| 2. Jones County, SD | 80% | 3% | Lakoma |
| 3. Tensas Parish, LA | 79% | 90% | Sharkey |
| 4. Issaquena County, MS | 79% | 90% | Sharkey |
| 5. Lyman County, SD | 79% | 4% | Millboro |
| 6. Collin County, TX | 78% | <1% | Houston Black |
| 7. Menard County, TX | 77% | <1% | Tarrant |
| 8. Sharkey County, MS | 77% | >99% | Sharkey |
| 9. Madison Parish, LA | 75% | 96% | Sharkey |
| 10. Assumption Parish, LA | 74% | >99% | Barbary |
| 11. Sutton County, TX | 73% | <1% | Tarrant |
| 12. Haakon County, SD | 72% | 3% | Ottumwa |
| 13. Concordia Parish, LA | 70% | 92% | Sharkey |
| 14. Ellis County, TX | 70% | <1% | Houston Black |
| 15. Kimble County, TX | 68% | <1% | Tarrant |
| 16. Tunica County, MS | 66% | 84% | Sharkey |
| 17. Williamson County, TX | 66% | <1% | Eckrant |
| 18. Schleicher County, TX | 66% | <1% | Tarrant |
| 19. Iberville Parish, LA | 66% | 99% | Sharkey |
| 20. Bell County, TX | 65% | <1% | Houston Black |
| 21. Washington County, MS | 65% | 87% | Sharkey |
| 22. Paulding County, OH | 64% | 93% | Paulding |
| 23. Nueces County, TX | 63% | 13% | Victoria |
| 24. Crittenden County, AR | 62% | 81% | Sharkey |
| 25. Kerr County, TX | 62% | <1% | Eckrant |
Three kinds of clay country
Most counties on the list fall into three groups. River bottoms of the lower Mississippi, in Louisiana, Mississippi and Arkansas, where floods laid down fine clay for thousands of years. The Blackland Prairie of Texas, with its dark, deep clays. And the western Dakotas, where soils formed from soft shale.
Clay holds water and nutrients well, which makes it fertile, but it drains slowly, packs hard when walked on wet, and cracks when it dries. Adding compost every year does more for clay than adding sand, which can make it set like concrete.
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- All mapped land in the 50 states and DC in the current soil survey.
- Method
- County rankings include counties with at least 100,000 acres of mapped land and soil ratings on at least 80% of it, so a small county with one unusual map unit cannot top the list. Counties without a full report on this site are named but not linked; the ZIP lookup covers them. Texture is the USDA texture class of the first mineral horizon, grouped into clayey (40% clay or more, or a clay texture class), sandy (70% sand or more with under 15% clay: sands and loamy sands), loamy (everything in between) and organic (peat and muck). Full methodology.