Collin County, Texas
Shrink-swell clay limits houses without basements on 72% of Collin County's mapped land, a higher share than 98% of US counties and the 9th highest of 254 Texas counties. A shallow water table limits basements on 1%.
100% of the county is in drought on the November 3, 2026 Drought Monitor map. FEMA's flood data list 82 flood losses here since 2016, 0% of them in buildings with basements. 10% of homes were built before 1980, against 50% nationally; the median home dates from 2003.
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 Collin County
| Expansive clay (limits slab homes) | 72.3% |
| High water table (limits basements) | 1.0% |
| Septic fields very limited | 81.0% |
| Clay swell (LEP, by area) | 10.0% |
| High-swell land (LEP 6%+) | 61.4% |
| Mapped soil | 567,142 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Houston Black | 39% | 91% |
| Heiden | 14% | 80% |
| Austin | 11% | 93% |
| Tinn | 6% | n/a |
| Altoga | 4% | n/a |
| Eddy | 3% | 0% |
How we count · survey areas TX085 (2025-09-04)
What the numbers mean here
Clay swell averages a linear extensibility of 10.0% by land area here, and 61% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 72% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 72% of Collin County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 31.24 in, 9.81 in below the 1991-2020 average year of 41.05 in.
USDA rates 81% 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 29 of the last 52 weeks; the most was 100% of its area, in 11 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 | 27.4% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
82 flood losses since 2016, $1.8 million paid. The worst year was 2018, with 17. Foundations of the buildings, where recorded: 100% slabs. Median water depth outside the building: 5 in.
| Year | Flood losses |
|---|---|
| 2016 | 12 |
| 2017 | 4 |
| 2018 | 17 |
| 2019 | 8 |
| 2020 | 12 |
| 2021 | 11 |
| 2022 | 4 |
| 2023 | 0 |
| 2024 | 10 |
| 2025 | 3 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 41.05 in |
| 12 months to August 2026 | 31.24 in (-9.81) |
| 2025 | 39.48 in (-1.57) |
| Wettest year since 1895 | 2015: 70.11 in |
| Driest year since 1895 | 1910: 20.64 in |
| Days with 1 inch or more, normal at LAVON DAM (12 mi away) | 11.9 |
Homes
| Housing units | 437,396 |
| Median year built | 2003 |
| Built before 1980 | 10% |
| Built 2000 or later | 57% |
| Owner-occupied | 65% |
| Median value, owner-occupied | $475,600 |
| Single-family detached | 68% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Cities in Collin County
| City | Expansive clay | High water table | Homes |
|---|---|---|---|
| Allen | 78% | under 1% | 39,094 |
| Anna | 76% | under 1% | 8,111 |
| Blue Ridge | 85% | 4% | 399 |
| Celina | 81% | 1% | 11,152 |
| Fairview | 71% | 1% | 4,552 |
| Farmersville | 66% | under 1% | 1,671 |
| Frisco | 76% | under 1% | 80,353 |
| Josephine | 84% | under 1% | 1,954 |
| Lavon | 80% | under 1% | 2,144 |
| Lowry Crossing | 72% | under 1% | 498 |
| Lucas | 76% | under 1% | 2,856 |
| McKinney | 73% | under 1% | 77,617 |
| Melissa | 69% | under 1% | 6,266 |
| Murphy | 80% | under 1% | 6,030 |
| Nevada | 82% | 0% | 476 |
| New Hope | 49% | under 1% | 285 |
| Parker | 69% | under 1% | 1,625 |
| Plano | 75% | under 1% | 117,686 |
| Princeton | 83% | under 1% | 8,130 |
| Prosper | 77% | under 1% | 11,921 |
| St. Paul | 84% | 0% | 315 |
| Weston | 77% | under 1% | 91 |
| Wylie | 56% | 1% | 19,511 |
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Rockwall County, TX | 23 mi | 72% | 2% |
| Hunt County, TX | 29 mi | 78% | 17% |
| Grayson County, TX | 30 mi | 60% | 4% |
| Denton County, TX | 31 mi | 50% | 1% |
| Dallas County, TX | 32 mi | 51% | 6% |
| Fannin County, TX | 39 mi | 66% | 23% |
| Kaufman County, TX | 43 mi | 73% | 16% |
| Cooke County, TX | 48 mi | 38% | under 1% |
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