Marion County, Iowa · Knoxville
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Marion County averages 54 nights a year at 20°F or colder, mostly November to March, and 30% of its homes predate 1960.
Heavy rain days of an inch or more come about 6.1 times a year here, most often in July. A sump pump that hasn't run since last season is a common weak point.
Sewage backups in Marion County spike on heavy-rain days, about 6.1 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 92 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
20% of occupied homes in Marion County heat mainly with wood or propane, close to the Iowa county median of 22.1%.
About 39 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 14,386 homes and around 33,642 residents, Marion County is 554 square miles of southern Iowa. Knoxville is the county seat; Pella, Pleasantville and Melcher-Dallas are the next largest communities. Half the homes here were built before 1975, half after.
26/100 Water Damage Risk Index: Moderate Marion County ranks 98 of 99 Iowa counties. See the statewide ranking and method.The three factors where Marion County ranks highest compared with other Iowa counties.
Winters here are on the gentler end for Iowa, and pipes still freeze. In the 2015–2024 record the county logged about 54 nights a year at or below 20°F (71st of 99) and 130 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
Cold snaps are the real risk. The worst in the record lasted 16 days below freezing (ending January 2018), and the low bottomed out near -23°F on January 31, 2019.
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 19 and end around Apr 23.
Marion gets fewer downpours than most Iowa counties, but they still fill basements. The county gets about 35.3 inches of rain and melted snow a year, with 6.1 days of an inch or more (83rd of 99). Those downpours cluster in July, September and October, when sump pumps and gutters are tested hardest. The wettest day on record brought 2.94 inches on July 29, 2015. The worst three-day stretch dropped 4.48 inches, ending July 29, 2015, the kind of soaking that overwhelms sump pumps and storm sewers.
The temperature crosses 32°F in both directions on roughly 92 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
61% of homes in Marion County predate 1980, below the Iowa county median of 72.8%, which ranks 88th of Iowa's 99 counties.
Growth since 2000 added 19% 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.
Beyond water
Marion County averages 39 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 expectBy main heating fuel, Marion County homes break down as 60% utility gas, 19% electric, 18% propane and 2% 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 Marion County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Jasper gets more pipe-freeze nights than Marion. Lucas County has the oldest housing nearby, with 75% of homes built before 1980.
By the numbers
| Factor | Marion | Iowa median | Rank |
|---|---|---|---|
| Homes built before 1960 | 30% | 48% | 91 of 99 |
| Homes built before 1980 | 61% | 73% | 88 of 99 |
| Homes built 2000 or later | 19% | 13% | 17 of 99 |
| Manufactured or mobile homes | 5% | 3.2% | 20 of 99 |
| Vacant homes | 7.4% | 9.5% | 80 of 99 |
| Wood or propane heat | 20% | 22% | 64 of 99 |
| Nights at 20°F or colder | 54/yr | 62/yr | 71 of 99 |
| Days with 1 inch+ of rain | 6.1/yr | 7.1/yr | 83 of 99 |
| Freeze-thaw days | 92/yr | 94/yr | 67 of 99 |
| Muggy nights (65°F+) | 39/yr | 29/yr | 15 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 Marion County: freezing from November to March, heavy rain in July, September 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