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St. Martin Parish, Louisiana
A shallow water table limits basements on 84% of St. Martin Parish's mapped land, a higher share than 92% of US counties. Shrink-swell clay limits houses without basements on 57%.
91.8% of the county is in drought on the October 13, 2026 Drought Monitor map, up from 64.4% a week earlier. FEMA's flood data list 551 flood losses here since 2016, 0% of them in buildings with basements. 42% of homes were built before 1980, against 50% nationally; the median home dates from 1986.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under St. Martin Parish
| Expansive clay (limits slab homes) | 57.5% |
| High water table (limits basements) | 84.4% |
| Septic fields very limited | 83.3% |
| Clay swell (LEP, by area) | 12.8% |
| High-swell land (LEP 6%+) | 57.5% |
| Mapped soil | 523,546 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Fausse | 18% | n/a |
| Dowling | 12% | n/a |
| Convent | 10% | n/a |
| Sharkey | 9% | 99% |
| Schriever | 5% | n/a |
| Dundee | 4% | n/a |
How we count · survey areas LA099 (2025-08-28)
What the numbers mean here
Clay swell averages a linear extensibility of 12.8% by land area here, and 57% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 57% of the mapped land.
Clay shrinks as it dries: 91.8% of the county is in drought on the latest map, and 57% of St. Martin Parish's mapped land has shrink-swell clay.
On 84% of St. Martin Parish's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 52.78 in, 9.19 in below the 1991-2020 average year of 61.97 in.
USDA rates 83% of the land very limited for septic absorption fields.
Drought
91.8% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 40 of the last 52 weeks; the most was 98.2% of its area, on the April 21, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 91.8% |
| D2 severe or worse | 13% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
551 flood losses since 2016, $21.8 million paid. The worst year was 2016, with 323. Foundations of the buildings, where recorded: 69% slabs, 5% crawl spaces, 25% elevated. Median water depth outside the building: 9 in.
| Year | Flood losses |
|---|---|
| 2016 | 323 |
| 2017 | 24 |
| 2018 | 8 |
| 2019 | 130 |
| 2020 | 4 |
| 2021 | 13 |
| 2022 | 0 |
| 2023 | 1 |
| 2024 | 32 |
| 2025 | 7 |
| 2026 to date | 9 |
Rain
| Average year, 1991-2020 | 61.97 in |
| 12 months to August 2026 | 52.78 in (-9.19) |
| 2025 | 59.11 in (-2.86) |
| Wettest year since 1895 | 1946: 83.39 in |
| Driest year since 1895 | 1924: 38.05 in |
| Days with 1 inch or more, normal at JEANERETTE 5 NW (13 mi away) | 19.9 |
Homes
| Housing units | 23,828 |
| Median year built | 1986 |
| Built before 1980 | 42% |
| Built 2000 or later | 32% |
| Owner-occupied | 78% |
| Median value, owner-occupied | $164,200 |
| Single-family detached | 70% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Iberville Parish, LA | 18 mi | 54% | 88% |
| Lafayette Parish, LA | 28 mi | 8% | 79% |
| West Baton Rouge Parish, LA | 30 mi | 44% | 81% |
| St. Mary Parish, LA | 35 mi | 52% | 80% |
| Assumption Parish, LA | 36 mi | 68% | 88% |
| Iberia Parish, LA | 38 mi | 31% | 84% |
| St. Landry Parish, LA | 39 mi | 41% | 84% |
| Pointe Coupee Parish, LA | 41 mi | 20% | 73% |
Sources: USDA SSURGO (August 28, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status