Rock County, Wisconsin · Janesville
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With 37% of homes built before 1960 and about 56 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
Basements flood here mostly in September. Rock County averages 7.2 days a year with an inch of rain or more.
Sewage backups in Rock County spike on heavy-rain days, about 7.2 a year, when sewer mains fill up and water finds the lowest drain.
Rock County's wettest day in the 2015–2024 record brought 3.23 inches, and about 89 freeze-thaw days a year mean ice dams in some winters.
10% of occupied homes in Rock County heat mainly with wood or propane, below the Wisconsin county median of 32.9%.
About 24 nights a year here stay at 65°F or warmer, so basements and crawl spaces can grow mold even without a leak.
Local risk profile
About 164,350 people live in Rock County, 718 square miles in southern Wisconsin, in roughly 71,109 homes. Janesville is the county seat; Beloit, Edgerton and Evansville are the next largest communities. The county's median home was built in 1970.
55/100 Water Damage Risk Index: Elevated Rock County ranks 26 of 72 Wisconsin counties. See the statewide ranking and method.The three factors where Rock County ranks highest compared with other Wisconsin counties.
Rock County is milder than most of Wisconsin, but not mild enough to skip winterizing. From 2015–2024 it averaged 56 nights a year at 20°F or colder, the range where pipes in exterior walls, crawl spaces and unheated garages freeze, and 136 nights at or below 32°F. That ranks 66th of 72 counties.
On January 31, 2019 the low fell to about -28°F, and in the stretch ending February 2019 the county went 17 days in a row below freezing. Leaks from split pipes typically appear the day the thaw arrives.
Most freezing nights fall from November to March, peaking in January. Disconnect garden hoses and shut off outdoor spigots before the first hard frost, and keep the heat at 55°F or higher if you'll be away.
On average the first fall freeze arrives around Oct 21 and the last spring freeze around May 3.
Heavy rain is a bigger factor here than in most of Wisconsin. Of roughly 38.8 inches of yearly precipitation, the damage comes from the 7.2 days a year with an inch or more, ranked 23rd of 72. July, August and September see the most. The single wettest day in the record: 3.23 inches, September 12, 2022. Multi-day storms matter most for basements; the wettest three days on record here totaled 4.7 inches (through September 13, 2022).
About 89 days a year swing from below freezing at night to above freezing by day. Those freeze-thaw cycles feed ice dams on roofs, open cracks in foundations and driveways, and stress pipes that are already marginal.
Housing
Wisconsin's 72 counties range widely in housing age; Rock ranks 7th, with 65% of its homes built before 1980.
Before 1960 is when 37% of these homes went up. Galvanized supply lines and cast iron drains were standard then, and after 60-plus years both corrode and crack, often out of sight inside a wall or under a slab.
Beyond water
Rock County averages 24 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in June. Keep indoor humidity under 60%, as the EPA advises, and dry any leak within 24 to 48 hours; in a humid month a wet basement left alone won't dry by itself.
Mold remediation: what to expectHeating fuel matters for fire risk. In Rock County it's 70% utility gas, 18% electric, 8% propane and 1% wood. Fires here are likelier to start in the kitchen or the wiring than in the furnace. After any fire, keep the HVAC off until ducts are checked, or soot will travel through the house.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Rock County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Dane, Green and Jefferson get more pipe-freeze nights than Rock. Its housing is the oldest in the area by share of homes built before 1980.
By the numbers
| Factor | Rock | Wisconsin median | Rank |
|---|---|---|---|
| Homes built before 1960 | 37% | 31% | 22 of 72 |
| Homes built before 1980 | 65% | 54% | 7 of 72 |
| Homes built 2000 or later | 16% | 21% | 65 of 72 |
| Manufactured or mobile homes | 2.6% | 4.8% | 56 of 72 |
| Vacant homes | 5.5% | 12% | 59 of 72 |
| Wood or propane heat | 9.5% | 33% | 61 of 72 |
| Nights at 20°F or colder | 56/yr | 73/yr | 66 of 72 |
| Days with 1 inch+ of rain | 7.2/yr | 6.3/yr | 23 of 72 |
| Freeze-thaw days | 89/yr | 94/yr | 65 of 72 |
| Muggy nights (65°F+) | 24/yr | 11/yr | 1 of 72 |
Rank 1 is the highest value. Bars run from the lowest to the highest Wisconsin county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Rock County: freezing from November to March, heavy rain in July, August and September.
Sources: U.S. Census Bureau, ACS 2024 5-year estimates (2020-2024); weather from NOAA nClimGrid-Daily county averages (EpiNOAA), 2015–2024, averaged across the county; county boundaries from Census TIGER. Reviewed 2026-10-21. Methodology