Riley County, Kansas
Shrink-swell clay limits houses without basements on 76% of Riley County's mapped land, a higher share than 98% of US counties. A shallow water table limits basements on 22%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 68 flood losses here since 2016, 36% of them in buildings with basements. 46% of homes were built before 1980, against 50% nationally; the median home dates from 1984.
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 Riley County
| Expansive clay (limits slab homes) | 75.9% |
| High water table (limits basements) | 21.8% |
| Septic fields very limited | 95.9% |
| Clay swell (LEP, by area) | 6.8% |
| High-swell land (LEP 6%+) | 70.1% |
| Mapped soil | 398,400 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Clime | 17% | n/a |
| Wymore | 15% | 100% |
| Irwin | 14% | n/a |
| Sogn | 6% | n/a |
| Reading | 5% | n/a |
| Tully | 4% | n/a |
How we count · survey areas KS161 (2025-08-26)
What the numbers mean here
Clay swell averages a linear extensibility of 6.8% by land area here, and 70% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 76% of the mapped land.
On 22% of Riley 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: 36.85 in, 3.45 in above the 1991-2020 average year of 33.40 in.
USDA rates 96% 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 6 of the last 52 weeks; the most was 8.3% of its area, in 6 weeks, most recently on the November 25, 2025 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
68 flood losses since 2016, $4.6 million paid. The worst year was 2018, with 40. Foundations of the buildings, where recorded: 36% basements, 28% slabs, 11% crawl spaces, 25% elevated. Median water depth outside the building: 15 in.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 1 |
| 2018 | 40 |
| 2019 | 20 |
| 2020 | 0 |
| 2021 | 1 |
| 2022 | 1 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 2 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 33.40 in |
| 12 months to August 2026 | 36.85 in (+3.45) |
| 2025 | 29.45 in (-3.95) |
| Wettest year since 1895 | 1951: 55.36 in |
| Driest year since 1895 | 1966: 17.28 in |
| Days with 1 inch or more, normal at TUTTLE CREEK LAKE (8 mi away) | 9.8 |
Homes
| Housing units | 30,755 |
| Median year built | 1984 |
| Built before 1980 | 46% |
| Built 2000 or later | 31% |
| Owner-occupied | 46% |
| Median value, owner-occupied | $237,100 |
| Single-family detached | 50% |
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 |
|---|---|---|---|
| Geary County, KS | 20 mi | 71% | 6% |
| Pottawatomie County, KS | 22 mi | 71% | 35% |
| Clay County, KS | 24 mi | 67% | 2% |
| Marshall County, KS | 36 mi | 72% | 73% |
| Wabaunsee County, KS | 37 mi | 73% | 27% |
| Dickinson County, KS | 37 mi | 81% | 3% |
| Washington County, KS | 39 mi | 67% | 6% |
| Morris County, KS | 42 mi | 82% | 10% |
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