Jefferson County, Wisconsin · Jefferson
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With 38% of homes built before 1960 and about 58 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
June brings the most downpours to Jefferson County, part of 7.1 heavy-rain days a year. Check the sump first.
38% of homes here predate 1960, when clay and cast iron sewer laterals were standard. Roots and cracks in those lines are a common cause of backups.
Jefferson County's wettest day in the 2015–2024 record brought 3.9 inches, and about 90 freeze-thaw days a year mean ice dams in some winters.
13% of occupied homes in Jefferson County heat mainly with wood or propane, below the Wisconsin county median of 32.9%.
With 20 muggy nights a year, mold in Jefferson County can appear within days of a leak. Dry first, then clean.
Local risk profile
With 36,890 homes and around 86,003 residents, Jefferson County is 556 square miles of southeast Wisconsin. Besides Jefferson, the county seat, the biggest communities are Watertown, Fort Atkinson and Lake Mills. Half the homes here were built before 1973, half after.
55/100 Water Damage Risk Index: Elevated Jefferson County ranks 24 of 72 Wisconsin counties. See the statewide ranking and method.The three factors where Jefferson County ranks highest compared with other Wisconsin counties.
Winters here are on the gentler end for Wisconsin, and pipes still freeze. It averaged 139 freezing nights a year over 2015–2024, 58 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 72 Wisconsin counties that's 65th.
The longest cold spell was straight 16 days without the temperature rising above freezing, ending in January 2018. The coldest night reached about -28°F on January 31, 2019. Burst pipes usually show up when a spell like that breaks and the ice thaws.
Expect the hardest freezes in January, inside a season that runs November to March. That's when an outdoor spigot left connected to a hose, or a pipe in a crawl space, is most likely to split.
Freezing nights typically start around Oct 20 and end around May 2.
Rainfall is about average for Wisconsin. The county gets about 37.4 inches of rain and melted snow a year, with 7.1 days of an inch or more (25th of 72). Those downpours cluster in June, August and September, when sump pumps and gutters are tested hardest. The wettest day on record brought 3.9 inches on September 12, 2022. The worst three-day stretch dropped 5.14 inches, ending September 13, 2022, the kind of soaking that overwhelms sump pumps and storm sewers.
About 90 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
59% of homes in Jefferson County predate 1980, above the Wisconsin county median of 54.1%, which ranks 22nd of Wisconsin's 72 counties.
In Jefferson County 38% of homes are older than 1960. If yours is one of them and the plumbing has never been replaced, expect galvanized steel supply pipe and cast iron drain lines, the two materials most likely to fail quietly.
Beyond water
Jefferson County averages 20 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 Jefferson County it's 67% utility gas, 17% electric, 11% propane and 3% 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 Jefferson County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Dane and Dodge get more pipe-freeze nights than Jefferson. Rock County has the oldest housing nearby, with 65% of homes built before 1980.
By the numbers
| Factor | Jefferson | Wisconsin median | Rank |
|---|---|---|---|
| Homes built before 1960 | 38% | 31% | 18 of 72 |
| Homes built before 1980 | 59% | 54% | 22 of 72 |
| Homes built 2000 or later | 20% | 21% | 44 of 72 |
| Manufactured or mobile homes | 3.6% | 4.8% | 48 of 72 |
| Vacant homes | 5.5% | 12% | 59 of 72 |
| Wood or propane heat | 13% | 33% | 56 of 72 |
| Nights at 20°F or colder | 58/yr | 73/yr | 65 of 72 |
| Days with 1 inch+ of rain | 7.1/yr | 6.3/yr | 25 of 72 |
| Freeze-thaw days | 90/yr | 94/yr | 59 of 72 |
| Muggy nights (65°F+) | 20/yr | 11/yr | 9 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 Jefferson County: freezing from November to March, heavy rain in June, 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