Original research
Expansive soil by county
How much of each state and county sits on high shrink-swell clay, from the USDA's detailed soil survey.
Written by HyreFoundation Research Desk Primary-source research and fact checking
The finding
An expansive soil map by county, built from the USDA's detailed soil survey (SSURGO): 15.1% of the rated soil acres in the U.S. have high or very high shrink-swell potential, meaning a linear extensibility of 6% or more in the top meter.
Another 24.7% are moderate. The states with the largest high-shrink-swell share are Kansas (44.2%), South Dakota (41.6%), Louisiana (41%), Missouri (36.6%), Texas (32.9%).
At county level, Stanley County, South Dakota (95.5%), Jones County, South Dakota (95.3%) and Hunt County, Texas (94%) are almost entirely high-shrink-swell soil. The full list of 3,363 soil survey areas is in the CSV.
The headline numbers
What is expansive soil, and how is it measured?
Expansive soil is clay that swells when wet and shrinks when dry. NRCS measures it as linear extensibility (LEP).
LEP is the change in length of a soil clod as it dries from moist to oven-dry.
NRCS rates shrink-swell potential as low under 3%, moderate from 3 to 6%, high from 6 to 9% and very high above 9%.
Above 3%, it says, shrinking and swelling can damage buildings, roads and other structures, and special design is commonly needed (NRCS Field Office Technical Guide, physical properties).
A house on this soil rises and drops with the seasons. Uneven movement is what cracks slabs and walls. See expansive clay soil and why foundations move.
Which counties have the highest share of expansive soil?
Soil survey areas of 50,000 rated acres or more, ranked by the share with high or very high shrink-swell potential. Most survey areas are one county; some combine two or more.
| Soil survey area | High or very high | Very high | Moderate | Rated acres |
|---|---|---|---|---|
| Stanley County, South Dakota | 95.5% | 91% | 2.1% | 906,594 |
| Jones County, South Dakota | 95.3% | 55% | 1.7% | 613,006 |
| Lyman County, South Dakota | 95.2% | 90.8% | 1.6% | 1,024,037 |
| Hunt County, Texas | 94% | 48.2% | 6% | 475,825 |
| Humphreys County, Mississippi | 92.1% | 62% | 7.3% | 243,557 |
| Navarro County, Texas | 91% | 59.6% | 5.8% | 573,466 |
| Kaufman and Rockwall Counties, Texas | 90.7% | 52.5% | 6.4% | 513,067 |
| Fillmore County, Nebraska | 90.5% | 64% | 5.6% | 367,912 |
| Orleans Parish, Louisiana | 90.2% | 89% | 9.5% | 70,765 |
| St. Bernard Parish, Louisiana | 89.8% | 88.6% | 4% | 158,426 |
| Audrain County, Missouri | 89.6% | 66.2% | 2.8% | 443,648 |
| Haakon County, South Dakota | 88.8% | 45.8% | 7.3% | 1,151,619 |
| Matagorda County, Texas | 88.4% | 53.1% | 7.6% | 622,127 |
| Jackson County Area, South Dakota, Northern Part | 87.4% | 56.3% | 6% | 496,425 |
| Menard County, Texas | 86.7% | 0.1% | 7% | 515,030 |
| Shelby County, Missouri | 86.3% | 61.8% | 11.5% | 319,792 |
| Swisher County, Texas | 86% | 7.1% | 12% | 573,162 |
| Lamar and Delta Counties, Texas | 85.2% | 31.8% | 11.3% | 672,845 |
| Jefferson Parish, Louisiana | 84.4% | 69.1% | 11.6% | 125,268 |
| Monroe County, Missouri | 83.7% | 55.8% | 14.2% | 414,067 |
| Falls County, Texas | 83.7% | 43.4% | 6.1% | 443,956 |
| Long Valley Area, Arizona | 83.6% | 66.3% | 2.7% | 443,503 |
| Floyd County, Texas | 83.4% | 6.1% | 7.5% | 624,770 |
| Miami County, Kansas | 83.1% | 12.7% | 16.3% | 362,236 |
| Sharkey County, Mississippi | 83% | 75.1% | 16.3% | 257,456 |
| Tensas Parish, Louisiana | 82.8% | 77% | 8.5% | 370,873 |
| Clay County, Nebraska | 82.2% | 34.6% | 11.2% | 366,001 |
| York County, Nebraska | 82.2% | 10.9% | 7.9% | 366,976 |
| Randolph County, Missouri | 81.7% | 35.3% | 9.9% | 307,183 |
| St. Charles Parish, Louisiana | 80.8% | 47.1% | 16.8% | 144,896 |
Expansive soil share for every state
| State | High or very high | Very high | Moderate | Rated acres |
|---|---|---|---|---|
| Kansas | 44.2% | 11.1% | 36.7% | 51,629,697 |
| South Dakota | 41.6% | 21.4% | 35.1% | 48,024,800 |
| Louisiana | 41% | 27% | 20.2% | 23,669,174 |
| Missouri | 36.6% | 13% | 34% | 43,157,604 |
| Texas | 32.9% | 10.8% | 28.1% | 145,169,153 |
| Illinois | 27.6% | 0.8% | 54.8% | 33,896,985 |
| Oklahoma | 27.4% | 3% | 27.5% | 40,328,441 |
| Arkansas | 25.7% | 9.5% | 16.2% | 30,551,670 |
| Montana | 24.3% | 2.2% | 34.1% | 84,473,691 |
| Iowa | 23.6% | 2.5% | 62.4% | 35,236,556 |
| North Dakota | 21.1% | 8% | 42.4% | 44,041,609 |
| Mississippi | 20% | 11.7% | 11% | 28,450,774 |
| Oregon | 19.3% | 2.2% | 28.5% | 49,778,593 |
| Arizona | 17.3% | 3.3% | 25.7% | 58,310,843 |
| Colorado | 16.2% | 0.6% | 26.4% | 57,295,205 |
| New Mexico | 15.4% | 0.1% | 39.6% | 65,189,642 |
| Wyoming | 13.6% | 1.9% | 37.2% | 48,316,045 |
| California | 13.5% | 2.4% | 23.6% | 82,441,261 |
| Nebraska | 13% | 4% | 31.2% | 48,705,678 |
| Nevada | 12.6% | 0.3% | 28.2% | 61,402,557 |
| Minnesota | 11.7% | 4.2% | 37.7% | 45,675,839 |
| Ohio | 11% | 0% | 56.6% | 24,212,583 |
| Alabama | 10.2% | 3% | 17.9% | 28,085,926 |
| West Virginia | 9.7% | 0% | 12% | 12,196,123 |
| Kentucky | 8.9% | 0.6% | 32.3% | 22,728,299 |
| Wisconsin | 8.3% | 1.6% | 24.6% | 31,657,949 |
| Indiana | 8.1% | 0.2% | 56.4% | 21,915,966 |
| Idaho | 8% | 0.5% | 22.7% | 44,292,158 |
| Utah | 7.4% | 0.3% | 28.9% | 34,377,294 |
| Virginia | 6% | 0.6% | 22.2% | 21,084,573 |
| Hawaii | 5.5% | 4% | 9.3% | 3,148,922 |
| North Carolina | 4.8% | 0.8% | 11.7% | 27,808,482 |
| South Carolina | 4.2% | 0.4% | 12.6% | 18,531,679 |
| Michigan | 3.7% | 0.7% | 16.7% | 33,521,403 |
| Tennessee | 3.7% | 1.2% | 22.7% | 24,906,184 |
| Rhode Island | 3.3% | 3.3% | 0.7% | 631,938 |
| New York | 3.2% | 0.3% | 5.5% | 25,430,880 |
| Georgia | 3.1% | 0.2% | 6.5% | 33,862,642 |
| Florida | 2.3% | 0.1% | 5.2% | 30,578,273 |
| New Hampshire | 2.3% | 0.4% | 1% | 4,714,650 |
| Washington | 1.8% | 0% | 14.7% | 34,855,892 |
| Maryland | 1.7% | 0.1% | 10.2% | 5,544,136 |
| Vermont | 1.2% | 0% | 4.6% | 5,676,782 |
| Pennsylvania | 1% | 0% | 12.6% | 27,477,441 |
| Delaware | 0.5% | 0% | 5.9% | 907,921 |
| Alaska | 0.2% | 0% | 5.5% | 272,276,821 |
| Massachusetts | 0.2% | 0% | 0.6% | 4,294,371 |
| Connecticut | 0.1% | 0% | 1.2% | 2,557,103 |
| Maine | 0.1% | 0% | 5.5% | 18,873,804 |
| New Jersey | 0.1% | 0.1% | 10.3% | 4,043,168 |
| District of Columbia | 0% | 0% | 18.6% | 19,848 |
What this means for your house
A county share tells you how common expansive soil is, not what is under your lot. Two houses on the same street can sit on different soils. To check your own lot, look it up in the free NRCS Web Soil Survey or have a geotechnical engineer test it before building or major repair.
If you live on expansive soil, steady moisture around the foundation is the main defense: good drainage and grading, gutters that discharge away from the house, and no big swings from heavy watering to none. Cracks that keep widening need a licensed structural engineer. Our foundation cracks guide shows which ones to watch.
Method
USDA NRCS Soil Survey Geographic Database (SSURGO) through the Soil Data Access Tabular service, queried state by state on October 27, 2026.
For each soil component, we took the highest representative linear extensibility (lep_r) of any layer starting in the top 100 cm. Acres per component = map unit acres times component percent.
We summed component acres by LEP class for each soil survey area (legend areasymbol) and state. Shares are of rated acres: components with no LEP value, such as water, rock outcrop and some urban land, are left out.
Survey areas are not always counties. The analysis does not weight by where houses are, so a county with clay farmland and sandy towns can score high. Survey data is mapped at field scale and does not replace a site test.
How to cite or embed this data
You may reuse the figures and the CSV with attribution (CC BY 4.0). Link back to this page so readers can see the method.
Citation: HyreFoundation Research Desk. (2026). Expansive soil by county. HyreFoundation. Data from USDA NRCS SSURGO via Soil Data Access, retrieved October 27, 2026. https://hyrefoundation.com/research/expansive-soil-by-county/
Embed snippet (paste under your chart or table):<p>Source: <a href="https://hyrefoundation.com/research/expansive-soil-by-county/">Expansive soil by county</a>, HyreFoundation analysis of USDA NRCS SSURGO via Soil Data Access (retrieved October 27, 2026).</p>
Dataset: /research/expansive-soil-by-county.csv, built from the public source named above. Recompute it from the source if you need a later cut.
Questions
Where is expansive soil most common?
What counts as expansive soil here?
Does a high county share mean my house is on expansive soil?
Why are some counties combined?
Can I download the data?
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HyreFoundation Research Desk
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