Union County, Ohio · Marysville
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Union County averages 34 nights a year at 20°F or colder, mostly November to March, and 21% of its homes predate 1960.
June brings the most downpours to Union County, part of 5.1 heavy-rain days a year. Check the sump first.
21% of homes here predate 1960, when clay and cast iron sewer laterals were standard. Roots and cracks in those lines are a common cause of backups.
In Union County, 2.59 inches fell on the wettest day of the 2015–2024 record. Storms like that, and ice dams in snowy winters, cause most roof leaks.
21% of occupied homes in Union County heat mainly with wood or propane, above the Ohio county median of 15.9%.
With 37 muggy nights a year, mold in Union County can appear within days of a leak. Dry first, then clean.
Local risk profile
With 25,158 homes and around 67,324 residents, Union County is 432 square miles of western Ohio. The county seat is Marysville, and Richwood, New California and Milford Center round out the largest towns. Much of its housing is recent, with a median build year of 1996.
41/100 Water Damage Risk Index: Moderate Union County ranks 64 of 88 Ohio counties. See the statewide ranking and method.The three factors where Union County ranks highest compared with other Ohio counties.
Union is on the colder side of Ohio for pipes. It averaged 107 freezing nights a year over 2015–2024, 34 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 88 Ohio counties that's 21st.
On February 24, 2015 the low fell to about -8°F, and in the stretch ending March 2015 the county went 18 days in a row below freezing. Leaks from split pipes typically appear the day the thaw arrives.
Most freezing nights fall from November to March, 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.
On average the first fall freeze arrives around Oct 27 and the last spring freeze around Apr 21.
Union gets fewer downpours than most Ohio counties, but they still fill basements. The county gets about 40.3 inches of rain and melted snow a year, with 5.1 days of an inch or more (59th of 88). Those downpours cluster in February, March and June, when sump pumps and gutters are tested hardest. The wettest day on record brought 2.59 inches on May 19, 2020. Multi-day storms matter most for basements; the wettest three days on record here totaled 3.3 inches (through September 10, 2018).
The temperature crosses 32°F in both directions on roughly 81 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
Roughly 36% of the county's housing was built before 1980. That puts Union among the newer housing stocks of Ohio's 88 counties.
Growth since 2000 added 44% 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
Union County averages 37 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in June. 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 Union County it's 53% utility gas, 23% electric, 20% propane and 2% wood. Propane heat is more common here than the state median. Have chimneys swept and fuel-burning appliances serviced each fall, and keep three feet clear around stoves and space heaters.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Union County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Champaign and Logan get more pipe-freeze nights than Union. Marion County has the oldest housing nearby, with 74% of homes built before 1980.
By the numbers
| Factor | Union | Ohio median | Rank |
|---|---|---|---|
| Homes built before 1960 | 21% | 37% | 83 of 88 |
| Homes built before 1980 | 36% | 61% | 86 of 88 |
| Homes built 2000 or later | 44% | 17% | 2 of 88 |
| Manufactured or mobile homes | 3.8% | 5.9% | 63 of 88 |
| Vacant homes | 3.7% | 8.4% | 88 of 88 |
| Wood or propane heat | 21% | 16% | 30 of 88 |
| Nights at 20°F or colder | 34/yr | 31/yr | 21 of 88 |
| Days with 1 inch+ of rain | 5.1/yr | 5.7/yr | 59 of 88 |
| Freeze-thaw days | 81/yr | 82/yr | 52 of 88 |
| Muggy nights (65°F+) | 37/yr | 35/yr | 32 of 88 |
Rank 1 is the highest value. Bars run from the lowest to the highest Ohio county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Union County: freezing from November to March, heavy rain in February, March and June.
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