Knox County, Missouri
A shallow water table limits basements on 85% of Knox County's mapped land, a higher share than 92% of US counties. Shrink-swell clay limits houses without basements on 81%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no 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 Knox County
| Expansive clay (limits slab homes) | 81.2% |
| High water table (limits basements) | 85.0% |
| Septic fields very limited | 99.7% |
| Clay swell (LEP, by area) | 8.3% |
| High-swell land (LEP 6%+) | 74.5% |
| Mapped soil | 324,262 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Armstrong | 19% | over 99% |
| Kilwinning | 15% | n/a |
| Leonard | 10% | n/a |
| Putnam | 10% | n/a |
| Lindley | 8% | n/a |
| Blackoar | 6% | n/a |
How we count · survey areas MO103 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 8.3% by land area here, and 74% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 81% of the mapped land.
On 85% of Knox 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: 35.29 in, 5.04 in below the 1991-2020 average year of 40.33 in.
USDA rates over 99% 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 21 of the last 52 weeks; the most was 100% of its area, in 3 weeks, most recently on the March 10, 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
FEMA's flood data list no flood losses in Knox County since 2016.
Rain
| Average year, 1991-2020 | 40.33 in |
| 12 months to August 2026 | 35.29 in (-5.04) |
| 2025 | 31.15 in (-9.18) |
| Wettest year since 1895 | 1973: 61.71 in |
| Driest year since 1895 | 1988: 17.90 in |
| Days with 1 inch or more, normal at EDINA (2 mi away) | 10.8 |
Homes
| Housing units | 1,937 |
| Median year built | 1965 |
| Built before 1980 | 72% |
| Built 2000 or later | 13% |
| Owner-occupied | 85% |
| Median value, owner-occupied | $101,400 |
| 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 |
|---|---|---|---|
| Scotland County, MO | 21 mi | 70% | 76% |
| Lewis County, MO | 22 mi | 63% | 81% |
| Shelby County, MO | 24 mi | 87% | 91% |
| Adair County, MO | 24 mi | 68% | 95% |
| Clark County, MO | 29 mi | 58% | 78% |
| Schuyler County, MO | 30 mi | 72% | 84% |
| Macon County, MO | 31 mi | 80% | 95% |
| Marion County, MO | 35 mi | 53% | 69% |
Sources: USDA SSURGO (September 2, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status