Suffolk County, New York
USDA's soil survey flags shrink-swell clay on 0% of Suffolk County's mapped land and a shallow water table under basements on 9%, both below the national shares of 15% and 29%. None of the county is in drought on the September 22, 2026 Drought Monitor map, after 6.5% a week earlier.
FEMA's flood data list 1,430 flood losses here since 2016, 37% of them in buildings with basements. 68% of homes were built before 1980, against 50% nationally; the median home dates from 1970.
Data as of September 22, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, September 22, 2026
of homes built before 1980
Soil under Suffolk County
| Expansive clay (limits slab homes) | 0.0% |
| High water table (limits basements) | 8.9% |
| Septic fields very limited | 59.6% |
| Clay swell (LEP, by area) | 0.9% |
| High-swell land (LEP 6%+) | 0.0% |
| Urban land, not rated | 1.1% |
| Mapped soil | 731,148 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Riverhead | 17% | n/a |
| Plymouth | 15% | n/a |
| Haven | 12% | n/a |
| Carver | 7% | n/a |
| Montauk | 4% | n/a |
| Bridgehampton | 2% | n/a |
How we count · survey areas NY103 (2025-08-27)
What the numbers mean here
Rain over the 12 months to August 2026: 39.64 in, 5.82 in below the 1991-2020 average year of 45.46 in.
USDA rates 60% of the land very limited for septic absorption fields.
With shrink-swell clay on 0% and a shallow water table on 9% of the land, the soil survey points to neither problem across most of Suffolk County; conditions still vary lot by lot.
Drought
0% of the county is in drought (D1 or worse) on the September 22, 2026 map. Part of the county was in drought in 40 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the July 14, 2026 map.
| Category, September 22, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 68.5% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
1,430 flood losses since 2016, $44.5 million paid. The worst year was 2024, with 494. Foundations of the buildings, where recorded: 37% basements, 19% slabs, 25% crawl spaces, 19% elevated. Median water depth outside the building: 11 in.
| Year | Flood losses |
|---|---|
| 2016 | 44 |
| 2017 | 143 |
| 2018 | 171 |
| 2019 | 84 |
| 2020 | 51 |
| 2021 | 138 |
| 2022 | 76 |
| 2023 | 180 |
| 2024 | 494 |
| 2025 | 30 |
| 2026 to date | 19 |
Rain
| Average year, 1991-2020 | 45.46 in |
| 12 months to August 2026 | 39.64 in (-5.82) |
| 2025 | 35.09 in (-10.37) |
| Wettest year since 1895 | 1983: 61.70 in |
| Driest year since 1895 | 1965: 29.31 in |
| Days with 1 inch or more, normal at RIVERHEAD RSCH FARM (2 mi away) | 12.1 |
Homes
| Housing units | 580,772 |
| Median year built | 1970 |
| Built before 1980 | 68% |
| Built 2000 or later | 13% |
| Owner-occupied | 82% |
| Median value, owner-occupied | $578,400 |
| Single-family detached | 80% |
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 |
|---|---|---|---|
| South Central Connecticut Planning Region, CT | 25 mi | 0% | 23% |
| Greater Bridgeport Planning Region, CT | 32 mi | 0% | 23% |
| Lower Connecticut River Valley Planning Region, CT | 35 mi | under 1% | 38% |
| Naugatuck Valley Planning Region, CT | 45 mi | under 1% | 37% |
| Western Connecticut Planning Region, CT | 46 mi | 0% | 35% |
| Southeastern Connecticut Planning Region, CT | 48 mi | 0% | 38% |
| Nassau County, NY | 49 mi | 0% | 18% |
| Westchester County, NY | 57 mi | 0% | 33% |
Sources: USDA SSURGO (August 27, 2025) · US Drought Monitor (September 22, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status