Grundy County, Illinois · Morris
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Grundy County averages 43 nights a year at 20°F or colder, mostly November to March, and 20% of its homes predate 1960.
Heavy rain days of an inch or more come about 6 times a year here, most often in June. A sump pump that hasn't run since last season is a common weak point.
20% 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.
In Grundy County, 4.12 inches fell on the wettest day of the 2015–2024 record. Storms like that, and ice dams in snowy winters, cause most roof leaks.
8% of occupied homes in Grundy County heat mainly with wood or propane, below the Illinois county median of 16.5%.
With 38 muggy nights a year, mold in Grundy County can appear within days of a leak. Dry first, then clean.
Local risk profile
Grundy County covers 418 square miles of northeast Illinois, with about 53,219 residents and 21,384 homes. Besides Morris, the county seat, the biggest communities are Minooka, Coal City and Gardner. Much of its housing is recent, with a median build year of 1990.
28/100 Water Damage Risk Index: Moderate Grundy County ranks 101 of 102 Illinois counties. See the statewide ranking and method.The three factors where Grundy County ranks highest compared with other Illinois counties.
Grundy is on the colder side of Illinois for pipes. It averaged 120 freezing nights a year over 2015–2024, 43 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 26th.
The longest cold spell was straight 19 days without the temperature rising above freezing, ending in March 2015. The coldest night reached about -22°F on January 30, 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.
On average the first fall freeze arrives around Oct 27 and the last spring freeze around Apr 22.
Grundy gets fewer downpours than most Illinois counties, but they still fill basements. Of roughly 38.2 inches of yearly precipitation, the damage comes from the 6 days a year with an inch or more, ranked 101st of 102. May, June and July see the most. The single wettest day in the record: 4.12 inches, September 28, 2019. Multi-day storms matter most for basements; the wettest three days on record here totaled 4.9 inches (through September 30, 2019).
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 88 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
Illinois's 102 counties range widely in housing age; Grundy ranks 98th, with 42% of its homes built before 1980.
Growth since 2000 added 36% of today's homes. In houses that new, the weak points are washing machine hoses, ice maker lines, water heaters and sump pumps rather than the pipes in the walls.
About 23% of homes went up between 1980 and 1999. Some houses from the late 1970s to the mid-1990s were plumbed with polybutylene, a gray plastic pipe known for failing at fittings. A plumber can tell you in a few minutes whether you have it.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 38 times a year here, below the Illinois county median of 51. Mold grows when indoor humidity stays above about 60%, the EPA's ceiling. A basement dehumidifier set to 50% and drying anything wet within 24 to 48 hours prevents most problems.
Mold remediation: what to expectBy main heating fuel, Grundy County homes break down as 77% utility gas, 14% electric, 8% propane and under 1% wood. Heating equipment, cooking and electrical failures cause most home fires nationally. Even a small kitchen fire can leave soot through the whole house, because smoke follows air currents into closets, ducts and attic space.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Grundy County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Kendall and LaSalle get more pipe-freeze nights than Grundy. All of its neighbors see more heavy-rain days. Livingston County has the oldest housing nearby, with 75% of homes built before 1980.
By the numbers
| Factor | Grundy | Illinois median | Rank |
|---|---|---|---|
| Homes built before 1960 | 20% | 38% | 97 of 102 |
| Homes built before 1980 | 42% | 66% | 98 of 102 |
| Homes built 2000 or later | 36% | 15% | 2 of 102 |
| Manufactured or mobile homes | 3.9% | 5.6% | 62 of 102 |
| Vacant homes | 3.7% | 11% | 99 of 102 |
| Wood or propane heat | 7.8% | 17% | 81 of 102 |
| Nights at 20°F or colder | 43/yr | 35/yr | 26 of 102 |
| Days with 1 inch+ of rain | 6/yr | 8.4/yr | 101 of 102 |
| Freeze-thaw days | 88/yr | 81/yr | 19 of 102 |
| Muggy nights (65°F+) | 38/yr | 51/yr | 78 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 Grundy County: freezing from November to March, heavy rain in May, June 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