Harrison County, Iowa · Logan
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Harrison County averages 60 nights a year at 20°F or colder, mostly November to March, and 53% of its homes predate 1960.
Heavy rain days of an inch or more come about 7.4 times a year here, most often in September. A sump pump that hasn't run since last season is a common weak point.
Sewage backups in Harrison County spike on heavy-rain days, about 7.4 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 95 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
28% of occupied homes in Harrison County heat mainly with wood or propane, above the Iowa county median of 22.1%.
About 38 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
With 6,698 homes and around 14,632 residents, Harrison County is 697 square miles of western Iowa. Logan is the county seat; Missouri Valley, Woodbine and Dunlap are the next largest communities. It has some of the oldest housing in the state: the median home went up in 1954.
66/100 Water Damage Risk Index: Elevated Harrison County ranks 9 of 99 Iowa counties. See the statewide ranking and method.The three factors where Harrison County ranks highest compared with other Iowa counties.
Pipe-freeze risk in Harrison County sits near the middle of the state. From 2015–2024 it averaged 60 nights a year at 20°F or colder, the range where pipes in exterior walls, crawl spaces and unheated garages freeze, and 135 nights at or below 32°F. That ranks 52nd of 99 counties.
Cold snaps are the real risk. The worst in the record lasted 22 days below freezing (ending March 2019), and the low bottomed out near -25°F on February 16, 2021.
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 20 and end around Apr 22.
Rainfall is about average for Iowa. About 7.4 days a year bring an inch or more (34th of 99), most often in September, out of 32.5 inches of total precipitation. On August 20, 2018, 4.71 inches fell in a single day. The worst three-day stretch dropped 5.91 inches, ending August 21, 2018, the kind of soaking that overwhelms sump pumps and storm sewers.
The temperature crosses 32°F in both directions on roughly 95 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; Harrison ranks 53rd, with 72% of its homes built before 1980.
53% were built before 1960. Homes from that era often still have galvanized steel supply pipe, which rusts from the inside until it pinholes, and cast iron drains that crack with age. Slow leaks behind walls are a common start to water damage in these houses.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 38 times a year here, above the Iowa county median of 29. 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 Harrison County it's 35% utility gas, 34% electric, 27% propane and 2% wood. Propane heat is above the Iowa norm. Annual chimney and vent inspection, which the NFPA recommends, is one of the most effective fire-prevention habits for these homes.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Harrison County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Crawford, Monona and Shelby get more pipe-freeze nights than Harrison. It also has the most heavy-rain days in its area. Shelby County has the oldest housing nearby, with 79% of homes built before 1980.
By the numbers
| Factor | Harrison | Iowa median | Rank |
|---|---|---|---|
| Homes built before 1960 | 53% | 48% | 22 of 99 |
| Homes built before 1980 | 72% | 73% | 53 of 99 |
| Homes built 2000 or later | 14% | 13% | 48 of 99 |
| Manufactured or mobile homes | 4.6% | 3.2% | 24 of 99 |
| Vacant homes | 9.1% | 9.5% | 57 of 99 |
| Wood or propane heat | 28% | 22% | 34 of 99 |
| Nights at 20°F or colder | 60/yr | 62/yr | 52 of 99 |
| Days with 1 inch+ of rain | 7.4/yr | 7.1/yr | 34 of 99 |
| Freeze-thaw days | 95/yr | 94/yr | 29 of 99 |
| Muggy nights (65°F+) | 38/yr | 29/yr | 19 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 Harrison 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