Dallas County, Texas
Shrink-swell clay limits houses without basements on 51% of Dallas County's mapped land, a higher share than 91% of US counties. A shallow water table limits basements on 6%.
100% of the county is in drought on the November 3, 2026 Drought Monitor map. FEMA's flood data list 554 flood losses here since 2016, 2% of them in buildings with basements. 45% of homes were built before 1980, against 50% nationally; the median home dates from 1983.
Data as of November 3, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, November 3, 2026
of homes built before 1980
Soil under Dallas County
| Expansive clay (limits slab homes) | 51.3% |
| High water table (limits basements) | 6.3% |
| Septic fields very limited | 80.2% |
| Clay swell (LEP, by area) | 9.4% |
| High-swell land (LEP 6%+) | 48.2% |
| Urban land, not rated | 14.1% |
| Mapped soil | 580,448 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Houston Black | 12% | 91% |
| Trinity | 8% | n/a |
| Austin | 7% | 93% |
| Eddy | 5% | 0% |
| Heiden | 5% | 80% |
| Ferris | 4% | n/a |
How we count · survey areas TX113 (2025-09-04)
What the numbers mean here
Clay swell averages a linear extensibility of 9.4% by land area here, and 48% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 51% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 51% of Dallas County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 32.37 in, 7.18 in below the 1991-2020 average year of 39.55 in.
USDA rates 80% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the November 3, 2026 map. Part of the county was in drought in 25 of the last 52 weeks; the most was 100% of its area, in 12 weeks, most recently on the November 3, 2026 map.
| Category, November 3, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 5.5% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
554 flood losses since 2016, $21.5 million paid. The worst year was 2022, with 128. Foundations of the buildings, where recorded: 2% basements, 82% slabs, 12% crawl spaces, 4% elevated. Median water depth outside the building: 8 in.
| Year | Flood losses |
|---|---|
| 2016 | 39 |
| 2017 | 34 |
| 2018 | 105 |
| 2019 | 61 |
| 2020 | 19 |
| 2021 | 75 |
| 2022 | 128 |
| 2023 | 14 |
| 2024 | 27 |
| 2025 | 21 |
| 2026 to date | 31 |
Rain
| Average year, 1991-2020 | 39.55 in |
| 12 months to August 2026 | 32.37 in (-7.18) |
| 2025 | 40.41 in (+0.86) |
| Wettest year since 1895 | 2015: 66.79 in |
| Driest year since 1895 | 1963: 20.07 in |
| Days with 1 inch or more, normal at DALLAS LOVE FLD (7 mi away) | 12 |
Homes
| Housing units | 1,064,965 |
| Median year built | 1983 |
| Built before 1980 | 45% |
| Built 2000 or later | 27% |
| Owner-occupied | 51% |
| Median value, owner-occupied | $303,000 |
| Single-family detached | 52% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Cities in Dallas County
| City | Expansive clay | High water table | Homes |
|---|---|---|---|
| Addison | 28% | under 1% | 11,369 |
| Balch Springs | 45% | 34% | 9,110 |
| Cedar Hill | 37% | under 1% | 17,499 |
| Cockrell Hill | 5% | under 1% | 1,329 |
| Coppell | 58% | 11% | 16,028 |
| Dallas | 37% | 5% | 590,237 |
| DeSoto | 49% | under 1% | 21,718 |
| Duncanville | 31% | under 1% | 14,027 |
| Farmers Branch | 45% | 3% | 17,260 |
| Garland | 59% | under 1% | 86,216 |
| Glenn Heights | 75% | under 1% | 6,073 |
| Grand Prairie | 58% | 2% | 71,853 |
| Highland Park | 35% | under 1% | 3,667 |
| Hutchins | 55% | 1% | 1,880 |
| Irving | 65% | 10% | 102,512 |
| Lancaster | 68% | under 1% | 15,458 |
| Mesquite | 74% | 3% | 53,953 |
| Richardson | 52% | under 1% | 47,960 |
| Rowlett | 78% | under 1% | 24,216 |
| Sachse | 81% | under 1% | 10,862 |
| Seagoville | 74% | 12% | 5,692 |
| Sunnyvale | 78% | 6% | 2,792 |
| University Park | 33% | 0% | 7,444 |
| Wilmer | 72% | 2% | 1,848 |
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Rockwall County, TX | 23 mi | 72% | 2% |
| Ellis County, TX | 29 mi | 72% | 4% |
| Tarrant County, TX | 30 mi | 41% | 4% |
| Kaufman County, TX | 30 mi | 73% | 16% |
| Collin County, TX | 32 mi | 72% | 1% |
| Denton County, TX | 36 mi | 50% | 1% |
| Johnson County, TX | 43 mi | 51% | 4% |
| Hunt County, TX | 47 mi | 78% | 17% |
Sources: USDA SSURGO (September 4, 2025) · US Drought Monitor (November 3, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status