Mercer County, Missouri
Shrink-swell clay limits houses without basements on 79% of Mercer County's mapped land, a higher share than 99% of US counties and the 10th highest of 115 Missouri counties. A shallow water table limits basements on 62%.
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. 67% of homes were built before 1980, against 50% nationally; the median home dates from 1970.
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) | 79.0% |
| High water table (limits basements) | 62.2% |
| Septic fields very limited | 99.3% |
| Clay swell (LEP, by area) | 6.3% |
| High-swell land (LEP 6%+) | 50.2% |
| Mapped soil | 291,488 acres |
How we count · survey areas MO129 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 6.3% by land area here, and 50% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 79% of the mapped land.
On 62% 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: 37.92 in, 0.79 in below the 1991-2020 average year of 38.71 in.
USDA rates 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 5 of the last 52 weeks; the most was 100% of its area, on the March 3, 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 Mercer County since 2016.
Rain
| Average year, 1991-2020 | 38.71 in |
| 12 months to August 2026 | 37.92 in (-0.79) |
| 2025 | 33.51 in (-5.20) |
| Wettest year since 1895 | 1993: 59.26 in |
| Driest year since 1895 | 1988: 18.74 in |
| Days with 1 inch or more, normal at SPICKARD 7 W (14 mi away) | 10.6 |
Homes
| Housing units | 1,902 |
| Median year built | 1970 |
| Built before 1980 | 67% |
| Built 2000 or later | 17% |
| Owner-occupied | 81% |
| Median value, owner-occupied | $104,900 |
| Single-family detached | 84% |
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 |
|---|---|---|---|
| Grundy County, MO | 21 mi | 75% | 78% |
| Harrison County, MO | 23 mi | 66% | 68% |
| Decatur County, IA | 25 mi | 66% | 76% |
| Wayne County, IA | 25 mi | 77% | 80% |
| Sullivan County, MO | 28 mi | 82% | 61% |
| Putnam County, MO | 29 mi | 76% | 74% |
| Daviess County, MO | 38 mi | 79% | 87% |
| Ringgold County, IA | 42 mi | 76% | 77% |
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