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Mercer County, New Jersey
A shallow water table limits basements on 44% of Mercer County's mapped land, a higher share than 61% of US counties. 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 225 flood losses here since 2016, 57% of them in buildings with basements. 64% of homes were built before 1980, against 50% nationally; the median home dates from 1969.
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 Mercer County
| Expansive clay (limits slab homes) | 0.0% |
| High water table (limits basements) | 44.0% |
| Septic fields very limited | 83.3% |
| Clay swell (LEP, by area) | 2.0% |
| High-swell land (LEP 6%+) | 0.1% |
| Urban land, not rated | 4.0% |
| Mapped soil | 146,500 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Sassafras | 11% | n/a |
| Bucks | 9% | n/a |
| Matapeake | 5% | n/a |
| Othello | 4% | n/a |
| Penn | 4% | n/a |
| Quakertown | 4% | n/a |
How we count · survey areas NJ021 (2025-08-28)
What the numbers mean here
On 44% of Mercer 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: 40.02 in, 7.43 in below the 1991-2020 average year of 47.45 in.
USDA rates 83% of the land very limited for septic absorption fields.
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 42 of the last 52 weeks; the most was 100% of its area, in 36 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
225 flood losses since 2016, $11.8 million paid. The worst year was 2021, with 161. Foundations of the buildings, where recorded: 57% basements, 30% slabs, 5% crawl spaces, 9% elevated. Median water depth outside the building: 12.5 in.
| Year | Flood losses |
|---|---|
| 2016 | 12 |
| 2017 | 1 |
| 2018 | 19 |
| 2019 | 5 |
| 2020 | 4 |
| 2021 | 161 |
| 2022 | 3 |
| 2023 | 5 |
| 2024 | 12 |
| 2025 | 1 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 47.45 in |
| 12 months to August 2026 | 40.02 in (-7.43) |
| 2025 | 38.18 in (-9.27) |
| Wettest year since 1895 | 2018: 64.48 in |
| Driest year since 1895 | 1965: 29.87 in |
| Days with 1 inch or more, normal at HIGHTSTOWN 2 W (7 mi away) | 12.8 |
Homes
| Housing units | 151,138 |
| Median year built | 1969 |
| Built before 1980 | 64% |
| Built 2000 or later | 15% |
| Owner-occupied | 62% |
| Median value, owner-occupied | $377,700 |
| Single-family detached | 48% |
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 |
|---|---|---|---|
| Middlesex County, NJ | 19 mi | 0% | 53% |
| Somerset County, NJ | 20 mi | 0% | 44% |
| Bucks County, PA | 22 mi | under 1% | 52% |
| Hunterdon County, NJ | 22 mi | 0% | 31% |
| Burlington County, NJ | 28 mi | 1% | 61% |
| Monmouth County, NJ | 29 mi | under 1% | 40% |
| Philadelphia County, PA | 30 mi | 0% | 5% |
| Union County, NJ | 33 mi | 0% | 42% |
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