Mercer County, Illinois · Aledo
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With 48% of homes built before 1960 and about 48 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
Heavy rain days of an inch or more come about 7.2 times a year here, most often in July. A sump pump that hasn't run since last season is a common weak point.
Backups often follow heavy rain, which Mercer County gets about 7.2 days a year, when storm water overloads sewer mains and pushes up through the lowest drain in the house.
In Mercer County, 3.26 inches fell on the wettest day of the 2015–2024 record. Storms like that, and ice dams in snowy winters, cause most roof leaks.
24% of occupied homes in Mercer County heat mainly with wood or propane, above the Illinois county median of 16.5%.
About 40 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 7,285 homes and around 15,495 residents, Mercer County is 561 square miles of northwest Illinois. Aledo is the county seat; Viola, Windsor and Sherrard are the next largest communities. Half the homes here were built before 1962, half after.
61/100 Water Damage Risk Index: Elevated Mercer County ranks 17 of 102 Illinois counties. See the statewide ranking and method.The three factors where Mercer County ranks highest compared with other Illinois counties.
Mercer County gets more hard-freeze nights than most of Illinois. In the 2015–2024 record the county logged about 48 nights a year at or below 20°F (9th of 102) and 123 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
Cold snaps are the real risk. The worst in the record lasted 15 days below freezing (ending January 2018), and the low bottomed out near -27°F on January 31, 2019.
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.
Freezing nights typically start around Oct 25 and end around Apr 22.
Mercer gets fewer downpours than most Illinois counties, but they still fill basements. Of roughly 37.4 inches of yearly precipitation, the damage comes from the 7.2 days a year with an inch or more, ranked 76th of 102. June, July and September see the most. The single wettest day in the record: 3.26 inches, August 29, 2018. The worst three-day stretch dropped 3.72 inches, ending May 1, 2019, the kind of soaking that overwhelms sump pumps and storm sewers.
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 89 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
77% of homes in Mercer County predate 1980, above the Illinois county median of 65.9%, which ranks 13th of Illinois's 102 counties.
Before 1960 is when 48% 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
Summer nights that don't drop below 65°F, a good marker of humid air, come about 40 times a year here, below the Illinois county median of 51. 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 expectBy main heating fuel, Mercer County homes break down as 60% utility gas, 13% electric, 23% propane and 1% wood. Propane heat is more common here than the state median. Have chimneys swept and fuel-burning appliances serviced each fall, and keep three feet clear around stoves and space heaters.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Mercer County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Mercer gets more pipe-freeze nights than any of its neighbors. Warren County has the oldest housing nearby, with 84% of homes built before 1980.
By the numbers
| Factor | Mercer | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 48% | 38% | 22 of 102 |
| Homes built before 1980 | 77% | 66% | 13 of 102 |
| Homes built 2000 or later | 10% | 15% | 81 of 102 |
| Manufactured or mobile homes | 2.9% | 5.6% | 74 of 102 |
| Vacant homes | 9.9% | 11% | 61 of 102 |
| Wood or propane heat | 24% | 17% | 23 of 102 |
| Nights at 20°F or colder | 48/yr | 35/yr | 9 of 102 |
| Days with 1 inch+ of rain | 7.2/yr | 8.4/yr | 76 of 102 |
| Freeze-thaw days | 89/yr | 81/yr | 11 of 102 |
| Muggy nights (65°F+) | 40/yr | 51/yr | 73 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 Mercer County: freezing from November to March, heavy rain in June, July 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