Nassau County, New York
A shallow water table limits basements on 18% of Nassau County's mapped land. Shrink-swell clay limits houses without basements on 0%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 2,176 flood losses here since 2016, 60% of them in buildings with basements. 85% of homes were built before 1980, against 50% nationally; the median home dates from 1955.
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 Nassau County
| Expansive clay (limits slab homes) | 0.0% |
| High water table (limits basements) | 17.9% |
| Septic fields very limited | 40.5% |
| Clay swell (LEP, by area) | 1.2% |
| High-swell land (LEP 6%+) | 0.0% |
| Urban land, not rated | 36.6% |
| Mapped soil | 209,900 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Riverhead | 11% | n/a |
| Montauk | 10% | n/a |
| Ipswich | 3% | n/a |
| Enfield | 3% | n/a |
| Hempstead | 3% | n/a |
| Plymouth | 2% | n/a |
How we count · survey areas NY059 (2025-08-28)
What the numbers mean here
On 18% of Nassau County'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: 38.94 in, 6.66 in below the 1991-2020 average year of 45.60 in.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 28 of the last 52 weeks; the most was 100% of its area, in 19 weeks, most recently on the August 4, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 0% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
2,176 flood losses since 2016, $42.6 million paid. The worst year was 2023, with 727. Foundations of the buildings, where recorded: 60% basements, 19% slabs, 12% crawl spaces, 9% elevated. Median water depth outside the building: 9 in.
| Year | Flood losses |
|---|---|
| 2016 | 59 |
| 2017 | 47 |
| 2018 | 129 |
| 2019 | 52 |
| 2020 | 58 |
| 2021 | 289 |
| 2022 | 603 |
| 2023 | 727 |
| 2024 | 175 |
| 2025 | 23 |
| 2026 to date | 14 |
Rain
| Average year, 1991-2020 | 45.60 in |
| 12 months to August 2026 | 38.94 in (-6.66) |
| 2025 | 33.15 in (-12.45) |
| Wettest year since 1895 | 1983: 63.07 in |
| Driest year since 1895 | 1965: 26.40 in |
| Days with 1 inch or more, normal at NEW YORK JFK INTL AP (11 mi away) | 11.3 |
Homes
| Housing units | 479,044 |
| Median year built | 1955 |
| Built before 1980 | 85% |
| Built 2000 or later | 7% |
| Owner-occupied | 82% |
| Median value, owner-occupied | $684,700 |
| Single-family detached | 76% |
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 |
|---|---|---|---|
| Queens County, NY | 14 mi | 0% | 15% |
| Bronx County, NY | 16 mi | 0% | 9% |
| Kings County, NY | 20 mi | 0% | 17% |
| New York County, NY | 20 mi | 0% | 2% |
| Hudson County, NJ | 26 mi | 0% | 32% |
| Bergen County, NJ | 30 mi | 0% | 26% |
| Westchester County, NY | 30 mi | 0% | 33% |
| Richmond County, NY | 31 mi | 0% | 22% |
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