Shiawassee County, Michigan · Corunna
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With 41% of homes built before 1960 and about 44 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
June brings the most downpours to Shiawassee County, part of 4.8 heavy-rain days a year. Check the sump first.
Sewage backups in Shiawassee County spike on heavy-rain days, about 4.8 a year, when sewer mains fill up and water finds the lowest drain.
Shiawassee County's wettest day in the 2015–2024 record brought 2.52 inches, and about 90 freeze-thaw days a year mean ice dams in some winters.
24% of occupied homes in Shiawassee County heat mainly with wood or propane, below the Michigan county median of 29%.
Muggy summer nights, lows of 65°F or more, come about 22 times a year in Shiawassee County. Mold after a leak spreads fastest from June through August.
Local risk profile
With 30,354 homes and around 67,991 residents, Shiawassee County is 531 square miles of southwest Michigan. The county seat is Corunna, and Owosso, Durand and Perry round out the largest towns. The county's median home was built in 1969.
63/100 Water Damage Risk Index: Elevated Shiawassee County ranks 12 of 83 Michigan counties. See the statewide ranking and method.The three factors where Shiawassee County ranks highest compared with other Michigan counties.
Shiawassee County is milder than most of Michigan, but not mild enough to skip winterizing. From 2015–2024 it averaged 44 nights a year at 20°F or colder, the range where pipes in exterior walls, crawl spaces and unheated garages freeze, and 129 nights at or below 32°F. That ranks 58th of 83 counties.
Cold snaps are the real risk. The worst in the record lasted 18 days below freezing (ending March 2015), and the low bottomed out near -20°F on February 20, 2015.
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 23 and the last spring freeze around Apr 28.
Heavy rain is a bigger factor here than in most of Michigan. The county gets about 35.2 inches of rain and melted snow a year, with 4.8 days of an inch or more (20th of 83). Those downpours cluster in June, August and October, when sump pumps and gutters are tested hardest. The wettest day on record brought 2.52 inches on August 16, 2016. Multi-day storms matter most for basements; the wettest three days on record here totaled 4.28 inches (through June 27, 2021).
About 90 days a year swing from below freezing at night to above freezing by day. Those freeze-thaw cycles feed ice dams on roofs, open cracks in foundations and driveways, and stress pipes that are already marginal.
Housing
70% of homes in Shiawassee County predate 1980, above the Michigan county median of 58.4%, which ranks 9th of Michigan's 83 counties.
Before 1960 is when 41% 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 22 times a year here, above the Michigan county median of 10. 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, Shiawassee County homes break down as 60% utility gas, 11% electric, 21% propane and 3% 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 Shiawassee County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Genesee, Gratiot and Livingston get more pipe-freeze nights than Shiawassee. Saginaw County has the oldest housing nearby, with 71% of homes built before 1980.
By the numbers
| Factor | Shiawassee | Michigan median | Rank |
|---|---|---|---|
| Homes built before 1960 | 41% | 32% | 19 of 83 |
| Homes built before 1980 | 70% | 58% | 9 of 83 |
| Homes built 2000 or later | 12% | 16% | 72 of 83 |
| Manufactured or mobile homes | 6.4% | 7.3% | 51 of 83 |
| Vacant homes | 7.3% | 20% | 67 of 83 |
| Wood or propane heat | 24% | 29% | 52 of 83 |
| Nights at 20°F or colder | 44/yr | 54/yr | 58 of 83 |
| Days with 1 inch+ of rain | 4.8/yr | 3.9/yr | 20 of 83 |
| Freeze-thaw days | 90/yr | 95/yr | 59 of 83 |
| Muggy nights (65°F+) | 22/yr | 10/yr | 13 of 83 |
Rank 1 is the highest value. Bars run from the lowest to the highest Michigan county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Shiawassee County: freezing from November to March, heavy rain in June, August 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