Marion County, Illinois · Salem
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Marion County averages 25 nights a year at 20°F or colder, mostly December to February, and 33% of its homes predate 1960.
Heavy rain days of an inch or more come about 12 times a year here, most often in July. A sump pump that hasn't run since last season is a common weak point.
Sewage backups in Marion County spike on heavy-rain days, about 12 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.
18% of occupied homes in Marion County heat mainly with wood or propane, above the Illinois county median of 16.5%.
About 65 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
With 17,334 homes and around 37,000 residents, Marion County is 573 square miles of southern Illinois. Salem is the county seat; Centralia, Central City and Sandoval are the next largest communities. Half the homes here were built before 1973, half after.
49/100 Water Damage Risk Index: Elevated Marion County ranks 58 of 102 Illinois counties. See the statewide ranking and method.The three factors where Marion 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 25 nights a year at or below 20°F (74th of 102) and 88 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
Cold snaps are the real risk. The worst in the record lasted 14 days below freezing (ending January 2018), and the low bottomed out near -7°F on December 23, 2022.
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 12.
Heavy rain is a bigger factor here than in most of Illinois. The county gets about 47 inches of rain and melted snow a year, with 12 days of an inch or more (11th of 102). Those downpours cluster in April, July and August, when sump pumps and gutters are tested hardest. The wettest day on record brought 3.12 inches on September 9, 2018. The worst three-day stretch dropped 6.32 inches, ending August 16, 2016, the kind of soaking that overwhelms sump pumps and storm sewers.
The temperature crosses 32°F in both directions on roughly 71 days a year. Each cycle melts and refreezes water at roof edges and in foundation cracks, which is how ice dams and basement seepage get started.
Housing
62% of homes in Marion County predate 1980, close to the Illinois county median of 65.9%, which ranks 66th of Illinois's 102 counties.
Older and newer homes sit side by side here: 33% predate 1960 and 15% are from 2000 or later. Corroded pipe is the typical failure in the first group, burst supply hoses in the second.
23% date from 1980 to 1999, the window when polybutylene, a gray flexible plastic supply pipe, was used in some homes. It's prone to leaks at the fittings, so it's worth checking for in a house from those years.
17% of homes are manufactured or mobile homes, above the Illinois county median of 5.6%. Their water lines run under the floor behind the skirting, so a torn skirt or failed heat tape freezes them faster than lines in a site-built house.
Beyond water
Marion County averages 65 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in July. 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, Marion County homes break down as 53% utility gas, 28% electric, 17% 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 Marion County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Fayette gets more pipe-freeze nights than Marion. Fayette County has the oldest housing nearby, with 64% of homes built before 1980.
By the numbers
| Factor | Marion | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 33% | 38% | 75 of 102 |
| Homes built before 1980 | 62% | 66% | 66 of 102 |
| Homes built 2000 or later | 15% | 15% | 47 of 102 |
| Manufactured or mobile homes | 17% | 5.6% | 11 of 102 |
| Vacant homes | 11% | 11% | 53 of 102 |
| Wood or propane heat | 18% | 17% | 44 of 102 |
| Nights at 20°F or colder | 25/yr | 35/yr | 74 of 102 |
| Days with 1 inch+ of rain | 12/yr | 8.4/yr | 11 of 102 |
| Freeze-thaw days | 71/yr | 81/yr | 73 of 102 |
| Muggy nights (65°F+) | 65/yr | 51/yr | 33 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 Marion County: freezing from December to February, heavy rain in April, July and August.
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