Expansive Soil in Iowa: County Ratings
21 of the 99 rated counties in Iowa have a dominant shrink-swell rating of High or Very High. Each rating below is the NRCS shrink-swell class covering the largest share of the county's mapped soil acres, computed from USDA SSURGO data. Open a county for the full class breakdown and what it means for a slab foundation.
| County | Dominant class | High + Very High share | Survey coverage |
|---|---|---|---|
| Adair County | Moderate | 48% | 99% |
| Adams County | High | 72% | 99% |
| Allamakee County | Moderate | 26% | 96% |
| Appanoose County | High | 67% | 95% |
| Audubon County | Moderate | 7% | 100% |
| Benton County | Moderate | 1% | 99% |
| Black Hawk County | Moderate | 0% | 97% |
| Boone County | Moderate | 4% | 99% |
| Bremer County | Moderate | 1% | 98% |
| Buchanan County | Moderate | 1% | 99% |
| Buena Vista County | Moderate | 13% | 99% |
| Butler County | Moderate | 3% | 99% |
| Calhoun County | Moderate | 7% | 99% |
| Carroll County | Moderate | 2% | 99% |
| Cass County | Moderate | 30% | 99% |
| Cedar County | Moderate | 2% | 99% |
| Cerro Gordo County | Moderate | 6% | 97% |
| Cherokee County | Moderate | 9% | 99% |
| Chickasaw County | Moderate | 1% | 99% |
| Clarke County | High | 61% | 99% |
| Clay County | Moderate | 29% | 98% |
| Clayton County | Moderate | 20% | 97% |
| Clinton County | Moderate | 4% | 97% |
| Crawford County | Moderate | 2% | 99% |
| Dallas County | Moderate | 11% | 98% |
| Davis County | High | 61% | 99% |
| Decatur County | High | 53% | 98% |
| Delaware County | Moderate | 6% | 99% |
| Des Moines County | High | 59% | 93% |
| Dickinson County | Moderate | 7% | 93% |
| Dubuque County | Moderate | 14% | 98% |
| Emmet County | Moderate | 6% | 98% |
| Fayette County | Moderate | 6% | 99% |
| Floyd County | Moderate | 4% | 99% |
| Franklin County | Moderate | 3% | 99% |
| Fremont County | Moderate | 13% | 99% |
| Greene County | Moderate | 7% | 99% |
| Grundy County | Moderate | 2% | 100% |
| Guthrie County | Moderate | 32% | 99% |
| Hamilton County | Moderate | 28% | 99% |
| Hancock County | Moderate | 11% | 99% |
| Hardin County | Moderate | 3% | 99% |
| Harrison County | Moderate | 17% | 99% |
| Henry County | High | 72% | 99% |
| Howard County | Moderate | 6% | 100% |
| Humboldt County | Moderate | 4% | 99% |
| Ida County | Moderate | 2% | 99% |
| Iowa County | Moderate | 38% | 99% |
| Jackson County | Moderate | 19% | 97% |
| Jasper County | Moderate | 17% | 99% |
| Jefferson County | High | 68% | 99% |
| Johnson County | Moderate | 20% | 97% |
| Jones County | Moderate | 4% | 99% |
| Keokuk County | High | 58% | 99% |
| Kossuth County | Moderate | 13% | 99% |
| Lee County | High | 64% | 95% |
| Linn County | Moderate | 1% | 97% |
| Louisa County | Moderate | 31% | 95% |
| Lucas County | High | 69% | 99% |
| Lyon County | Moderate | 11% | 99% |
| Madison County | High | 63% | 97% |
| Mahaska County | High | 63% | 99% |
| Marion County | High | 58% | 94% |
| Marshall County | Moderate | 2% | 99% |
| Mills County | Moderate | 10% | 99% |
| Mitchell County | Moderate | 3% | 99% |
| Monona County | Moderate | 36% | 99% |
| Monroe County | High | 55% | 99% |
| Montgomery County | Moderate | 17% | 99% |
| Muscatine County | Moderate | 3% | 95% |
| O'Brien County | Moderate | 30% | 100% |
| Osceola County | Moderate | 15% | 99% |
| Page County | Moderate | 36% | 99% |
| Palo Alto County | Moderate | 6% | 99% |
| Plymouth County | Moderate | 2% | 99% |
| Pocahontas County | Moderate | 7% | 99% |
| Polk County | Moderate | 7% | 90% |
| Pottawattamie County | Moderate | 8% | 99% |
| Poweshiek County | Moderate | 27% | 99% |
| Ringgold County | High | 64% | 99% |
| Sac County | Moderate | 15% | 99% |
| Scott County | Moderate | 2% | 96% |
| Shelby County | Moderate | 2% | 100% |
| Sioux County | Moderate | 16% | 98% |
| Story County | Moderate | 5% | 99% |
| Tama County | Moderate | 4% | 99% |
| Taylor County | Moderate | 50% | 99% |
| Union County | Moderate | 47% | 98% |
| Van Buren County | High | 68% | 98% |
| Wapello County | High | 61% | 98% |
| Warren County | High | 64% | 98% |
| Washington County | High | 60% | 99% |
| Wayne County | High | 70% | 99% |
| Webster County | Moderate | 23% | 97% |
| Winnebago County | Moderate | 15% | 98% |
| Winneshiek County | Moderate | 13% | 99% |
| Woodbury County | Moderate | 15% | 98% |
| Worth County | Moderate | 8% | 98% |
| Wright County | Moderate | 22% | 99% |
How these ratings are computed
Ratings come from USDA NRCS SSURGO soil survey data: for each soil component we take the maximum linear extensibility percent (lep_r) in the top 100 cm, apply the NRCS Handbook Part 618 class limits (Low under 3 percent, Moderate 3 to 6, High 6 to 9, Very High 9 and above), assign map units by plurality of component percent, and roll acres up to the county. Full details on the methodology section of the lookup page. A county rating is not a parcel-level geotechnical assessment.