Madison County, Iowa
Shrink-swell clay limits houses without basements on 88% of Madison County's mapped land, a higher share than 100% of US counties and the 3rd highest of 99 Iowa counties. A shallow water table limits basements on 77%.
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. 55% of homes were built before 1980, against 50% nationally; the median home dates from 1977.
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 Madison County
| Expansive clay (limits slab homes) | 87.8% |
| High water table (limits basements) | 77.0% |
| Septic fields very limited | 95.7% |
| Clay swell (LEP, by area) | 6.6% |
| High-swell land (LEP 6%+) | 63.2% |
| Mapped soil | 360,400 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Sharpsburg | 21% | 98% |
| Ladoga | 10% | n/a |
| Gara | 10% | 65% |
| Macksburg | 8% | n/a |
| Lamoni | 7% | n/a |
| Shelby | 6% | n/a |
How we count · survey areas IA121 (2025-09-08)
What the numbers mean here
Clay swell averages a linear extensibility of 6.6% by land area here, and 63% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 88% of the mapped land.
On 77% of Madison 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: 37.45 in, 1.82 in above the 1991-2020 average year of 35.63 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. No part of the county was in drought in the last 52 weeks.
| 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 Madison County since 2016.
Rain
| Average year, 1991-2020 | 35.63 in |
| 12 months to August 2026 | 37.45 in (+1.82) |
| 2025 | 35.42 in (-0.21) |
| Wettest year since 1895 | 1993: 51.46 in |
| Driest year since 1895 | 1988: 18.64 in |
| Days with 1 inch or more, normal at INDIANOLA 2W (19 mi away) | 9.5 |
Homes
| Housing units | 7,100 |
| Median year built | 1977 |
| Built before 1980 | 55% |
| Built 2000 or later | 28% |
| Owner-occupied | 80% |
| Median value, owner-occupied | $245,100 |
| Single-family detached | 82% |
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 |
|---|---|---|---|
| Warren County, IA | 23 mi | 81% | 80% |
| Clarke County, IA | 24 mi | 74% | 78% |
| Adair County, IA | 24 mi | 91% | 80% |
| Union County, IA | 24 mi | 85% | 78% |
| Dallas County, IA | 24 mi | 17% | 60% |
| Polk County, IA | 34 mi | 13% | 52% |
| Guthrie County, IA | 35 mi | 62% | 66% |
| Lucas County, IA | 41 mi | 73% | 78% |
Sources: USDA SSURGO (September 8, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status