Olmsted County, Minnesota · Rochester
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Olmsted County averages 80 nights a year at 20°F or colder, mostly November to April, and 19% of its homes predate 1960.
Basements flood here mostly in July. Olmsted County averages 8.6 days a year with an inch of rain or more.
Sewage backups in Olmsted County spike on heavy-rain days, about 8.6 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 94 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
9% of occupied homes in Olmsted County heat mainly with wood or propane, below the Minnesota county median of 30%.
About 11 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
About 164,498 people live in Olmsted County, 654 square miles in southeast Minnesota, in roughly 71,151 homes. Besides Rochester, the county seat, the biggest communities are Stewartville, Byron and Eyota. Much of its housing is recent, with a median build year of 1989.
41/100 Water Damage Risk Index: Moderate Olmsted County ranks 67 of 87 Minnesota counties. See the statewide ranking and method.The three factors where Olmsted County ranks highest compared with other Minnesota counties.
Winters here are on the gentler end for Minnesota, and pipes still freeze. From 2015–2024 it averaged 80 nights a year at 20°F or colder, the range where pipes in exterior walls, crawl spaces and unheated garages freeze, and 161 nights at or below 32°F. That ranks 66th of 87 counties.
Cold snaps are the real risk. The worst in the record lasted 32 days below freezing (ending March 2019), and the low bottomed out near -36°F on January 31, 2019.
Most freezing nights fall from November to April, 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 11 and end around May 4.
Heavy rain is a bigger factor here than in most of Minnesota. The county gets about 37.1 inches of rain and melted snow a year, with 8.6 days of an inch or more (3rd of 87). Those downpours cluster in June, July and August, when sump pumps and gutters are tested hardest. The wettest day on record brought 3.42 inches on June 22, 2024. The worst three-day stretch dropped 4.4 inches, ending September 13, 2019, the kind of soaking that overwhelms sump pumps and storm sewers.
The temperature crosses 32°F in both directions on roughly 94 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
41% of homes in Olmsted County predate 1980, below the Minnesota county median of 58.4%, which ranks 77th of Minnesota's 87 counties.
Growth since 2000 added 35% 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.
25% 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.
Renters occupy 29% of homes. If you rent, the building is usually the landlord's to repair, but your belongings are only covered by renters insurance.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 11 times a year here, below the Minnesota county median of 13. 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 expectHeating fuel matters for fire risk. In Olmsted County it's 72% utility gas, 18% electric, 8% propane and under 1% 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 Olmsted County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Dodge gets more pipe-freeze nights than Olmsted. Mower County has the oldest housing nearby, with 74% of homes built before 1980.
By the numbers
| Factor | Olmsted | Minnesota median | Rank |
|---|---|---|---|
| Homes built before 1960 | 19% | 34% | 74 of 87 |
| Homes built before 1980 | 41% | 58% | 77 of 87 |
| Homes built 2000 or later | 35% | 21% | 5 of 87 |
| Manufactured or mobile homes | 2.6% | 3.8% | 58 of 87 |
| Vacant homes | 5.9% | 11% | 69 of 87 |
| Wood or propane heat | 8.5% | 30% | 80 of 87 |
| Nights at 20°F or colder | 80/yr | 89/yr | 66 of 87 |
| Days with 1 inch+ of rain | 8.6/yr | 5.3/yr | 3 of 87 |
| Freeze-thaw days | 94/yr | 86/yr | 3 of 87 |
| Muggy nights (65°F+) | 11/yr | 13/yr | 53 of 87 |
Rank 1 is the highest value. Bars run from the lowest to the highest Minnesota county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Olmsted County: freezing from November to April, heavy rain in June, 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