Allen County, Kansas
Shrink-swell clay limits houses without basements on 75% of Allen County's mapped land, a higher share than 98% of US counties. A shallow water table limits basements on 61%.
78.6% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 7 flood losses here since 2016. 72% of homes were built before 1980, against 50% nationally; the median home dates from 1965.
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 Allen County
| Expansive clay (limits slab homes) | 75.3% |
| High water table (limits basements) | 61.3% |
| Septic fields very limited | 99.1% |
| Clay swell (LEP, by area) | 7.7% |
| High-swell land (LEP 6%+) | 76.0% |
| Mapped soil | 323,386 acres |
How we count · survey areas KS001 (2025-08-26)
What the numbers mean here
Clay swell averages a linear extensibility of 7.7% by land area here, and 76% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 75% of the mapped land.
Clay shrinks as it dries: 78.6% of the county is in drought on the latest map, and 75% of Allen County's mapped land has shrink-swell clay.
On 61% of Allen 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: 38.18 in, 4.09 in below the 1991-2020 average year of 42.27 in.
USDA rates 99% of the land very limited for septic absorption fields.
Drought
78.6% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 29 of the last 52 weeks; the most was 100% of its area, in 2 weeks, most recently on the September 8, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 78.6% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
7 flood losses since 2016, $597,691 paid. The worst year was 2024, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 2 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 4 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 42.27 in |
| 12 months to August 2026 | 38.18 in (-4.09) |
| 2025 | 41.08 in (-1.19) |
| Wettest year since 1895 | 1973: 61.70 in |
| Driest year since 1895 | 1963: 20.21 in |
| Days with 1 inch or more, normal at IOLA 1 W (7 mi away) | 12.6 |
Homes
| Housing units | 6,077 |
| Median year built | 1965 |
| Built before 1980 | 72% |
| Built 2000 or later | 10% |
| Owner-occupied | 75% |
| Median value, owner-occupied | $107,600 |
| Single-family detached | 83% |
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 |
|---|---|---|---|
| Neosho County, KS | 22 mi | 72% | 64% |
| Anderson County, KS | 23 mi | 80% | 72% |
| Bourbon County, KS | 25 mi | 69% | 58% |
| Woodson County, KS | 25 mi | 73% | 72% |
| Wilson County, KS | 33 mi | 69% | 60% |
| Coffey County, KS | 34 mi | 77% | 76% |
| Linn County, KS | 34 mi | 78% | 61% |
| Crawford County, KS | 36 mi | 67% | 79% |
Sources: USDA SSURGO (August 26, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status