Monona County, Iowa · Onawa
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Monona County averages 64 nights a year at 20°F or colder, mostly November to March, and 54% of its homes predate 1960.
Heavy rain days of an inch or more come about 5.7 times a year here, most often in May. A sump pump that hasn't run since last season is a common weak point.
Sewage backups in Monona County spike on heavy-rain days, about 5.7 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 98 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
22% of occupied homes in Monona County heat mainly with wood or propane, close to the Iowa county median of 22.1%.
Muggy summer nights, lows of 65°F or more, come about 32 times a year in Monona County. Mold after a leak spreads fastest from June through August.
Local risk profile
About 8,557 people live in Monona County, 694 square miles in western Iowa, in roughly 4,372 homes. Besides Onawa, the county seat, the biggest communities are Mapleton, Whiting and Ute. It has some of the oldest housing in the state: the median home went up in 1956.
51/100 Water Damage Risk Index: Elevated Monona County ranks 45 of 99 Iowa counties. See the statewide ranking and method.The three factors where Monona County ranks highest compared with other Iowa counties.
Pipe-freeze risk in Monona County sits near the middle of the state. From 2015–2024 it averaged 64 nights a year at 20°F or colder, the range where pipes in exterior walls, crawl spaces and unheated garages freeze, and 141 nights at or below 32°F. That ranks 45th of 99 counties.
On February 16, 2021 the low fell to about -27°F, and in the stretch ending March 2019 the county went 32 days in a row below freezing. Leaks from split pipes typically appear the day the thaw arrives.
Expect the hardest freezes in January, inside a season that runs November to March. That's when an outdoor spigot left connected to a hose, or a pipe in a crawl space, is most likely to split.
Freezing nights typically start around Oct 18 and end around Apr 22.
Monona gets fewer downpours than most Iowa counties, but they still fill basements. About 5.7 days a year bring an inch or more (93rd of 99), most often in May, out of 30.3 inches of total precipitation. On August 20, 2018, 3.34 inches fell in a single day. The worst three-day stretch dropped 4.04 inches, ending September 25, 2015, the kind of soaking that overwhelms sump pumps and storm sewers.
The temperature crosses 32°F in both directions on roughly 98 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
Iowa's 99 counties range widely in housing age; Monona ranks 45th, with 74% of its homes built before 1980.
Before 1960 is when 54% 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
Monona County averages 32 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in May. The EPA recommends keeping indoor humidity below 60%, ideally 30 to 50%. Basements can pass 60% on their own in summer, so a dehumidifier matters even without a leak, and anything wet should be dried within 24 to 48 hours.
Mold remediation: what to expectHeating fuel matters for fire risk. In Monona County it's 37% utility gas, 35% electric, 20% propane and 2% 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 Monona County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Crawford and Woodbury get more pipe-freeze nights than Monona. All of its neighbors see more heavy-rain days. Crawford County has the oldest housing nearby, with 76% of homes built before 1980.
By the numbers
| Factor | Monona | Iowa median | Rank |
|---|---|---|---|
| Homes built before 1960 | 54% | 48% | 19 of 99 |
| Homes built before 1980 | 74% | 73% | 45 of 99 |
| Homes built 2000 or later | 11% | 13% | 71 of 99 |
| Manufactured or mobile homes | 5.8% | 3.2% | 14 of 99 |
| Vacant homes | 11% | 9.5% | 28 of 99 |
| Wood or propane heat | 22% | 22% | 54 of 99 |
| Nights at 20°F or colder | 64/yr | 62/yr | 45 of 99 |
| Days with 1 inch+ of rain | 5.7/yr | 7.1/yr | 93 of 99 |
| Freeze-thaw days | 98/yr | 94/yr | 3 of 99 |
| Muggy nights (65°F+) | 32/yr | 29/yr | 37 of 99 |
Rank 1 is the highest value. Bars run from the lowest to the highest Iowa county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Monona County: freezing from November to March, heavy rain in May, August 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