Washington County, Illinois · Nashville
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Washington County averages 24 nights a year at 20°F or colder, mostly December to February, and 37% of its homes predate 1960.
Basements flood here mostly in March. Washington County averages 11.5 days a year with an inch of rain or more.
Sewage backups in Washington County spike on heavy-rain days, about 11.5 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 71 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
28% of occupied homes in Washington County heat mainly with wood or propane, above the Illinois county median of 16.5%.
Muggy summer nights, lows of 65°F or more, come about 69 times a year in Washington County. Mold after a leak spreads fastest from June through August.
Local risk profile
Washington County covers 563 square miles of southern Illinois, with about 13,627 residents and 6,415 homes. The county seat is Nashville, and Okawville, Wamac and Irvington round out the largest towns. Half the homes here were built before 1972, half after.
53/100 Water Damage Risk Index: Elevated Washington County ranks 39 of 102 Illinois counties. See the statewide ranking and method.The three factors where Washington County ranks highest compared with other Illinois counties.
Winters here are on the gentler end for Illinois, and pipes still freeze. In the 2015–2024 record the county logged about 24 nights a year at or below 20°F (76th of 102) and 86 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
The longest cold spell was straight 14 days without the temperature rising above freezing, ending in January 2018. The coldest night reached about -6°F on January 2, 2018. Burst pipes usually show up when a spell like that breaks and the ice thaws.
The freeze season here runs December to February, with January the coldest. If you travel then, leave the thermostat at 55°F or above and open sink cabinets on outside walls.
Freezing nights typically start around Oct 25 and end around Apr 10.
Heavy rain is a bigger factor here than in most of Illinois. The county gets about 46 inches of rain and melted snow a year, with 11.5 days of an inch or more (16th of 102). Those downpours cluster in March, April and July, when sump pumps and gutters are tested hardest. The wettest day on record brought 3.56 inches on August 15, 2016. The worst three-day stretch dropped 7.21 inches, ending August 16, 2016, the kind of soaking that overwhelms sump pumps and storm sewers.
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 71 times a year here. They're the main driver of ice dams and of water working its way through foundation cracks in late winter.
Housing
63% of homes in Washington County predate 1980, close to the Illinois county median of 65.9%, which ranks 60th of Illinois's 102 counties.
The mix runs from 37% built before 1960 to 18% built since 2000, so older neighborhoods bring aging pipe while newer subdivisions bring failed appliance lines and water heaters.
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
Washington County averages 69 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in May. The EPA recommends keeping indoor humidity below 60%, ideally 30 to 50%. Basements can pass 60% on their own in summer, so a dehumidifier matters even without a leak, and anything wet should be dried within 24 to 48 hours.
Mold remediation: what to expectBy main heating fuel, Washington County homes break down as 37% utility gas, 32% electric, 26% propane and 2% wood. Propane heat is above the Illinois norm. Annual chimney and vent inspection, which the NFPA recommends, is one of the most effective fire-prevention habits for these homes.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Washington County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Marion gets more pipe-freeze nights than Washington. Randolph County has the oldest housing nearby, with 64% of homes built before 1980.
By the numbers
| Factor | Washington | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 37% | 38% | 58 of 102 |
| Homes built before 1980 | 63% | 66% | 60 of 102 |
| Homes built 2000 or later | 18% | 15% | 26 of 102 |
| Manufactured or mobile homes | 8.9% | 5.6% | 33 of 102 |
| Vacant homes | 9.7% | 11% | 63 of 102 |
| Wood or propane heat | 28% | 17% | 15 of 102 |
| Nights at 20°F or colder | 24/yr | 35/yr | 76 of 102 |
| Days with 1 inch+ of rain | 12/yr | 8.4/yr | 16 of 102 |
| Freeze-thaw days | 71/yr | 81/yr | 73 of 102 |
| Muggy nights (65°F+) | 69/yr | 51/yr | 24 of 102 |
Rank 1 is the highest value. Bars run from the lowest to the highest Illinois county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Washington 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