Iowa: basement moisture and foundation risk by county
99 counties, ranked by our combined index. Highest combined risk is Butler County (69), lowest is Harrison County (27). The worst soil for foundation cracks specifically is in Wayne County.
| County | Index | Moisture | Cracks | Water table | Region |
|---|---|---|---|---|---|
| Butler County | 69 | 68 | 52 | 95 | Des Moines Lobe and prairie potholes |
| Cerro Gordo County | 69 | 67 | 54 | 95 | Des Moines Lobe and prairie potholes |
| Humboldt County | 68 | 68 | 57 | 82 | Des Moines Lobe and prairie potholes |
| Hancock County | 66 | 65 | 57 | 82 | Des Moines Lobe and prairie potholes |
| Worth County | 66 | 68 | 51 | 82 | Des Moines Lobe and prairie potholes |
| Appanoose County | 65 | 53 | 69 | 82 | Dissected till plain with a claypan |
| Marshall County | 65 | 65 | 53 | 82 | Des Moines Lobe and prairie potholes |
| Emmet County | 64 | 64 | 42 | 95 | Des Moines Lobe and prairie potholes |
| Hardin County | 64 | 67 | 57 | 66 | Des Moines Lobe and prairie potholes |
| Boone County | 63 | 65 | 58 | 66 | Des Moines Lobe and prairie potholes |
| Franklin County | 63 | 65 | 48 | 82 | Des Moines Lobe and prairie potholes |
| Hamilton County | 63 | 68 | 53 | 66 | Des Moines Lobe and prairie potholes |
| Carroll County | 62 | 66 | 55 | 66 | Des Moines Lobe and prairie potholes |
| Webster County | 62 | 66 | 43 | 82 | Des Moines Lobe and prairie potholes |
| Buena Vista County | 61 | 56 | 53 | 82 | Wisconsinan till plain |
| Montgomery County | 61 | 53 | 68 | 66 | Dissected till plain with a claypan |
| Polk County | 61 | 53 | 57 | 82 | Wisconsinan till plain |
| Wayne County | 61 | 53 | 70 | 66 | Dissected till plain with a claypan |
| Calhoun County | 60 | 67 | 34 | 82 | Des Moines Lobe and prairie potholes |
| Jasper County | 60 | 57 | 49 | 82 | Wisconsinan till plain |
| Kossuth County | 60 | 65 | 48 | 66 | Des Moines Lobe and prairie potholes |
| Page County | 60 | 50 | 58 | 82 | Dissected till plain with a claypan |
| Van Buren County | 60 | 52 | 57 | 82 | Dissected till plain with a claypan |
| Wright County | 60 | 67 | 35 | 82 | Des Moines Lobe and prairie potholes |
| Adams County | 59 | 54 | 61 | 66 | Dissected till plain with a claypan |
| Greene County | 59 | 69 | 40 | 66 | Des Moines Lobe and prairie potholes |
| Henry County | 59 | 50 | 68 | 66 | Dissected till plain with a claypan |
| Howard County | 59 | 52 | 52 | 82 | Wisconsinan till plain |
| Madison County | 59 | 57 | 57 | 66 | Wisconsinan till plain |
| Pocahontas County | 59 | 64 | 34 | 82 | Des Moines Lobe and prairie potholes |
| Taylor County | 59 | 53 | 52 | 82 | Dissected till plain with a claypan |
| Winnebago County | 59 | 67 | 43 | 66 | Des Moines Lobe and prairie potholes |
| Floyd County | 58 | 67 | 39 | 66 | Des Moines Lobe and prairie potholes |
| Iowa County | 58 | 56 | 56 | 66 | Wisconsinan till plain |
| Lee County | 58 | 49 | 64 | 66 | Dissected till plain with a claypan |
| Lucas County | 58 | 53 | 48 | 82 | Dissected till plain with a claypan |
| Poweshiek County | 58 | 54 | 57 | 66 | Wisconsinan till plain |
| Adair County | 57 | 56 | 52 | 66 | Wisconsinan till plain |
| Audubon County | 57 | 52 | 56 | 66 | Wisconsinan till plain |
| Davis County | 57 | 51 | 48 | 82 | Dissected till plain with a claypan |
| Decatur County | 57 | 53 | 55 | 66 | Dissected till plain with a claypan |
| Grundy County | 57 | 53 | 45 | 82 | Wisconsinan till plain |
| Palo Alto County | 57 | 68 | 35 | 66 | Des Moines Lobe and prairie potholes |
| Sac County | 57 | 54 | 54 | 66 | Wisconsinan till plain |
| Story County | 57 | 64 | 41 | 66 | Des Moines Lobe and prairie potholes |
| Benton County | 56 | 54 | 51 | 66 | Wisconsinan till plain |
| Black Hawk County | 56 | 57 | 37 | 82 | Wisconsinan till plain |
| Chickasaw County | 56 | 55 | 51 | 66 | Wisconsinan till plain |
| Ringgold County | 56 | 53 | 52 | 66 | Dissected till plain with a claypan |
| Buchanan County | 55 | 56 | 45 | 66 | Wisconsinan till plain |
| Cass County | 55 | 54 | 49 | 66 | Wisconsinan till plain |
| Clinton County | 55 | 55 | 46 | 66 | Wisconsinan till plain |
| Dickinson County | 55 | 53 | 51 | 66 | Wisconsinan till plain |
| Scott County | 55 | 53 | 51 | 66 | Wisconsinan till plain |
| Jefferson County | 54 | 50 | 39 | 82 | Dissected till plain with a claypan |
| Johnson County | 54 | 54 | 45 | 66 | Wisconsinan till plain |
| Jones County | 54 | 52 | 47 | 66 | Wisconsinan till plain |
| Marion County | 54 | 55 | 32 | 82 | Wisconsinan till plain |
| Wapello County | 54 | 50 | 40 | 82 | Dissected till plain with a claypan |
| Keokuk County | 53 | 55 | 41 | 66 | Wisconsinan till plain |
| Mahaska County | 53 | 57 | 53 | 46 | Wisconsinan till plain |
| Muscatine County | 53 | 56 | 40 | 66 | Wisconsinan till plain |
| Winneshiek County | 53 | 54 | 41 | 66 | Wisconsinan till plain |
| Clarke County | 52 | 52 | 43 | 66 | Dissected till plain with a claypan |
| Monroe County | 52 | 49 | 47 | 66 | Dissected till plain with a claypan |
| Union County | 52 | 49 | 45 | 66 | Dissected till plain with a claypan |
| Warren County | 52 | 54 | 39 | 66 | Wisconsinan till plain |
| Bremer County | 51 | 56 | 49 | 46 | Wisconsinan till plain |
| Cedar County | 51 | 53 | 36 | 66 | Wisconsinan till plain |
| Clay County | 51 | 53 | 38 | 66 | Wisconsinan till plain |
| Des Moines County | 51 | 52 | 38 | 66 | Dissected till plain with a claypan |
| Guthrie County | 51 | 54 | 36 | 66 | Wisconsinan till plain |
| Mitchell County | 51 | 53 | 52 | 46 | Wisconsinan till plain |
| Dallas County | 50 | 56 | 43 | 46 | Wisconsinan till plain |
| Tama County | 50 | 53 | 34 | 66 | Wisconsinan till plain |
| Fayette County | 49 | 54 | 44 | 46 | Wisconsinan till plain |
| Louisa County | 48 | 56 | 39 | 46 | Wisconsinan till plain |
| Jackson County | 46 | 52 | 38 | 46 | Wisconsinan till plain |
| Washington County | 46 | 53 | 36 | 46 | Wisconsinan till plain |
| Linn County | 45 | 53 | 33 | 46 | Wisconsinan till plain |
| Osceola County | 35 | 34 | 41 | 30 | Loess hills |
| Ida County | 34 | 36 | 34 | 30 | Loess hills |
| Plymouth County | 34 | 35 | 35 | 30 | Loess hills |
| Dubuque County | 33 | 37 | 31 | 30 | Driftless Area |
| Lyon County | 33 | 33 | 36 | 30 | Loess hills |
| Pottawattamie County | 33 | 34 | 35 | 30 | Loess hills |
| Cherokee County | 32 | 33 | 31 | 30 | Loess hills |
| Monona County | 32 | 34 | 31 | 30 | Loess hills |
| Woodbury County | 32 | 35 | 29 | 30 | Loess hills |
| Crawford County | 31 | 34 | 38 | 16 | Loess hills |
| O'Brien County | 31 | 35 | 35 | 16 | Loess hills |
| Clayton County | 30 | 35 | 22 | 30 | Driftless Area |
| Fremont County | 30 | 35 | 22 | 30 | Loess hills |
| Delaware County | 29 | 34 | 20 | 30 | Driftless Area |
| Mills County | 29 | 34 | 22 | 30 | Loess hills |
| Allamakee County | 28 | 33 | 19 | 30 | Driftless Area |
| Shelby County | 28 | 34 | 29 | 16 | Loess hills |
| Harrison County | 27 | 33 | 28 | 16 | Loess hills |
| Sioux County | 27 | 33 | 27 | 16 | Loess hills |
Values from USDA NRCS SSURGO where available, otherwise our regional model — each county page states which. Methodology.
The physiographic regions inside Iowa
State lines are political; soil follows geology. These are the distinct ground types inside Iowa and why each behaves the way it does.
Wisconsinan till plain
The classic American basement belt. Below the topsoil sits dense till that water barely penetrates, so infiltrating water travels sideways along it until it meets the first vertical obstruction — typically a basement wall.
39 counties: Adair County, Audubon County, Benton County, Black Hawk County, Bremer County, Buchanan County, Buena Vista County, Cass County, Cedar County, Chickasaw County, Clay County, Clinton County, Dallas County, Dickinson County, Fayette County, Grundy County, Guthrie County, Howard County, Iowa County, Jackson County, Jasper County, Johnson County, Jones County, Keokuk County, Linn County, Louisa County, Madison County, Mahaska County, Marion County, Mitchell County, Muscatine County, Polk County, Poweshiek County, Sac County, Scott County, Tama County, Warren County, Washington County, Winneshiek County
Des Moines Lobe and prairie potholes
The youngest glaciation in the Midwest, so the landscape has not yet developed a drainage network. Without artificial drainage much of it would be wetland. A house in a depression and a house 300 m away on a rise have genuinely different risk — this is where a county average tells you least.
22 counties: Boone County, Butler County, Calhoun County, Carroll County, Cerro Gordo County, Emmet County, Floyd County, Franklin County, Greene County, Hamilton County, Hancock County, Hardin County, Humboldt County, Kossuth County, Marshall County, Palo Alto County, Pocahontas County, Story County, Webster County, Winnebago County, Worth County, Wright County
Dissected till plain with a claypan
The claypan is a hard clay layer a few tens of centimetres under the lawn. Water sits on it and spreads sideways. The typical symptom is seepage through the upper part of the wall rather than at the floor.
19 counties: Adams County, Appanoose County, Clarke County, Davis County, Decatur County, Des Moines County, Henry County, Jefferson County, Lee County, Lucas County, Monroe County, Montgomery County, Page County, Ringgold County, Taylor County, Union County, Van Buren County, Wapello County, Wayne County
Loess hills
Loess is permeable and the water table is deep, but it is prone to erosion and to collapse under load when wetted — a different failure mode from expansive clay. A broken downspout can undermine a loess footing.
15 counties: Cherokee County, Crawford County, Fremont County, Harrison County, Ida County, Lyon County, Mills County, Monona County, O'Brien County, Osceola County, Plymouth County, Pottawattamie County, Shelby County, Sioux County, Woodbury County
Driftless Area
The region the ice sheets missed. Slope, permeable loess, deep water table. Soil-driven basement risk is low here; the problems are surface runoff arriving from the hillside rather than groundwater pushing in.
4 counties: Allamakee County, Clayton County, Delaware County, Dubuque County
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