Rock County, Wisconsin
A shallow water table limits basements on 31% of Rock County's mapped land, a higher share than 50% of US counties. Shrink-swell clay limits houses without basements on 5%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 36 flood losses here since 2016, 57% of them in buildings with basements. 65% 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 Rock County
| Expansive clay (limits slab homes) | 4.6% |
| High water table (limits basements) | 31.3% |
| Septic fields very limited | 83.7% |
| Clay swell (LEP, by area) | 4.0% |
| High-swell land (LEP 6%+) | 6.7% |
| Mapped soil | 464,326 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Kidder | 10% | n/a |
| Plano | 10% | n/a |
| Warsaw | 6% | n/a |
| St. Charles | 5% | n/a |
| Dresden | 5% | n/a |
| Edmund | 4% | n/a |
How we count · survey areas WI105 (2025-09-10)
What the numbers mean here
On 31% of Rock 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: 35.12 in, 2.30 in below the 1991-2020 average year of 37.42 in.
USDA rates 84% 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 19 of the last 52 weeks; the most was 100% of its area, in 2 weeks, most recently on the June 9, 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
36 flood losses since 2016, $355,754 paid. The worst year was 2018, with 12. Foundations of the buildings, where recorded: 57% basements, 35% slabs, 4% crawl spaces, 4% elevated. Median water depth outside the building: 11.5 in.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 1 |
| 2018 | 12 |
| 2019 | 8 |
| 2020 | 4 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 1 |
| 2025 | 0 |
| 2026 to date | 10 |
Rain
| Average year, 1991-2020 | 37.42 in |
| 12 months to August 2026 | 35.12 in (-2.30) |
| 2025 | 32.39 in (-5.03) |
| Wettest year since 1895 | 2018: 49.22 in |
| Driest year since 1895 | 1901: 20.04 in |
| Days with 1 inch or more, normal at AFTON - JANESVILLE WWTP (2 mi away) | 8.8 |
Homes
| Housing units | 71,109 |
| Median year built | 1970 |
| Built before 1980 | 65% |
| Built 2000 or later | 16% |
| Owner-occupied | 71% |
| Median value, owner-occupied | $231,600 |
| Single-family detached | 74% |
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 |
|---|---|---|---|
| Winnebago County, IL | 23 mi | 9% | 28% |
| Green County, WI | 27 mi | 30% | 19% |
| Walworth County, WI | 27 mi | under 1% | 33% |
| Boone County, IL | 27 mi | 6% | 55% |
| Jefferson County, WI | 28 mi | 4% | 57% |
| Dane County, WI | 32 mi | 7% | 34% |
| Stephenson County, IL | 37 mi | 13% | 24% |
| McHenry County, IL | 40 mi | 2% | 54% |
Sources: USDA SSURGO (September 10, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status