Jefferson County, Missouri · Hillsboro
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With 15% of homes built before 1960 and about 24 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
April brings the most downpours to Jefferson County, part of 10.6 heavy-rain days a year. Check the sump first.
15% 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 3.75 inches, and about 71 freeze-thaw days a year mean ice dams in some winters.
9% of occupied homes in Jefferson County heat mainly with wood or propane, below the Missouri county median of 24.5%.
With 71 muggy nights a year, mold in Jefferson County can appear within days of a leak. Dry first, then clean.
Local risk profile
With 93,955 homes and around 229,458 residents, Jefferson County is 656 square miles of eastern Missouri. Besides Hillsboro, the county seat, the biggest communities are Arnold, Festus and Murphy. Much of its housing is recent, with a median build year of 1987.
40/100 Water Damage Risk Index: Moderate Jefferson County ranks 92 of 114 Missouri counties. See the statewide ranking and method.The three factors where Jefferson County ranks highest compared with other Missouri counties.
Pipe-freeze risk in Jefferson County sits near the middle of the state. It averaged 84 freezing nights a year over 2015–2024, 24 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 114 Missouri counties that's 70th.
The longest cold spell was straight 12 days without the temperature rising above freezing, ending in January 2018. The coldest night reached about -6°F on December 23, 2022. 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 December to February. 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 29 and end around Apr 6.
Rainfall is about average for Missouri. The county gets about 45.9 inches of rain and melted snow a year, with 10.6 days of an inch or more (50th of 114). Those downpours cluster in March, April and July, when sump pumps and gutters are tested hardest. The wettest day on record brought 3.75 inches on September 8, 2018. The worst three-day stretch dropped 6.73 inches, ending December 29, 2015, the kind of soaking that overwhelms sump pumps and storm sewers.
About 71 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
41% of homes in Jefferson County predate 1980, below the Missouri county median of 53%, which ranks 98th of Missouri's 114 counties.
Since 2000 the county has added enough housing that 29% of homes are that new. Modern PEX and copper rarely fail on their own; the leaks come from connections, appliances and storms.
The 1980s and 1990s account for 30% of the county's homes. If yours is from those decades, look under the sinks and at the water heater for gray plastic pipe stamped PB, which is polybutylene and leak-prone.
Manufactured and mobile homes make up 9% of the housing here. Water lines in the underbelly depend on intact skirting and working heat tape, and they're usually the first to freeze in a cold snap.
Beyond water
Jefferson County averages 71 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in May. 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 32% utility gas, 58% electric, 7% propane and 2% 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
Franklin, St. Francois and Washington get more pipe-freeze nights than Jefferson. St. Louis County has the oldest housing nearby, with 69% of homes built before 1980.
By the numbers
| Factor | Jefferson | Missouri median | Rank |
|---|---|---|---|
| Homes built before 1960 | 15% | 25% | 98 of 114 |
| Homes built before 1980 | 41% | 53% | 98 of 114 |
| Homes built 2000 or later | 29% | 21% | 17 of 114 |
| Manufactured or mobile homes | 9% | 9.8% | 68 of 114 |
| Vacant homes | 6% | 15% | 107 of 114 |
| Wood or propane heat | 9% | 25% | 103 of 114 |
| Nights at 20°F or colder | 24/yr | 28/yr | 70 of 114 |
| Days with 1 inch+ of rain | 11/yr | 10/yr | 50 of 114 |
| Freeze-thaw days | 71/yr | 77/yr | 95 of 114 |
| Muggy nights (65°F+) | 71/yr | 65/yr | 27 of 114 |
Rank 1 is the highest value. Bars run from the lowest to the highest Missouri 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 December to February, heavy rain in March, April and July.
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