McHenry County, Illinois · Woodstock
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Pipes freeze in McHenry County on about 51 nights a year, mostly November to March. Older homes, 18% of the stock here, are most at risk.
Heavy rain days of an inch or more come about 7.6 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 McHenry County spike on heavy-rain days, about 7.6 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 91 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
3% of occupied homes in McHenry County heat mainly with wood or propane, below the Illinois county median of 16.5%.
Muggy summer nights, lows of 65°F or more, come about 25 times a year in McHenry County. Mold after a leak spreads fastest from June through August.
Local risk profile
With 121,329 homes and around 312,591 residents, McHenry County is 603 square miles of northeast Illinois. Besides Woodstock, the county seat, the biggest communities are Crystal Lake, Algonquin and Lake in the Hills. Much of its housing is recent, with a median build year of 1989.
38/100 Water Damage Risk Index: Moderate McHenry County ranks 88 of 102 Illinois counties. See the statewide ranking and method.The three factors where McHenry County ranks highest compared with other Illinois counties.
McHenry County gets more hard-freeze nights than most of Illinois. It averaged 133 freezing nights a year over 2015–2024, 51 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 102 Illinois counties that's 6th.
The longest cold spell was straight 19 days without the temperature rising above freezing, ending in March 2015. The coldest night reached about -27°F on January 31, 2019. Burst pipes usually show up when a spell like that breaks and the ice thaws.
The freeze season here runs November to March, 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 21 and end around May 3.
Rainfall is about average for Illinois. Of roughly 38.5 inches of yearly precipitation, the damage comes from the 7.6 days a year with an inch or more, ranked 67th of 102. June, July and October see the most. The single wettest day in the record: 2.81 inches, September 13, 2019. The worst three-day stretch dropped 4.31 inches, ending September 4, 2018, the kind of soaking that overwhelms sump pumps and storm sewers.
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 91 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
38% of homes in McHenry County predate 1980, below the Illinois county median of 65.9%, which ranks 100th of Illinois's 102 counties.
Since 2000 the county has added enough housing that 26% 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 36% 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.
Beyond water
McHenry County averages 25 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 expectBy main heating fuel, McHenry County homes break down as 85% utility gas, 12% electric, 3% propane and under 1% wood. Most homes here heat with gas or electricity, so cooking and electrical faults are the likelier fire sources. Even a contained kitchen fire can send soot through the ductwork to every room.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across McHenry County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Boone gets more pipe-freeze nights than McHenry. It also has the most heavy-rain days in its area. Cook County has the oldest housing nearby, with 73% of homes built before 1980.
By the numbers
| Factor | McHenry | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 18% | 38% | 98 of 102 |
| Homes built before 1980 | 38% | 66% | 100 of 102 |
| Homes built 2000 or later | 26% | 15% | 12 of 102 |
| Manufactured or mobile homes | 0.7% | 5.6% | 100 of 102 |
| Vacant homes | 3.1% | 11% | 101 of 102 |
| Wood or propane heat | 2.8% | 17% | 95 of 102 |
| Nights at 20°F or colder | 51/yr | 35/yr | 6 of 102 |
| Days with 1 inch+ of rain | 7.6/yr | 8.4/yr | 67 of 102 |
| Freeze-thaw days | 91/yr | 81/yr | 3 of 102 |
| Muggy nights (65°F+) | 25/yr | 51/yr | 100 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 McHenry County: freezing from November to March, heavy rain in June, July and October.
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