Union County, Ohio
A shallow water table limits basements on 97% of Union County's mapped land, a higher share than 99% of US counties and the 3rd highest of 88 Ohio counties. Shrink-swell clay limits houses without basements on 25%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 3 flood losses here since 2016. 36% of homes were built before 1980, against 50% nationally; the median home dates from 1996.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Union County
| Expansive clay (limits slab homes) | 24.5% |
| High water table (limits basements) | 96.6% |
| Septic fields very limited | 98.3% |
| Clay swell (LEP, by area) | 4.8% |
| High-swell land (LEP 6%+) | 5.9% |
| Mapped soil | 279,488 acres |
How we count · survey areas OH159 (2025-09-08)
What the numbers mean here
Clay swell averages a linear extensibility of 4.8% by land area here, and 6% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 25% of the mapped land.
On 97% of Union County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 40.32 in, 0.94 in above the 1991-2020 average year of 39.38 in.
USDA rates 98% of the land very limited for septic absorption fields.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 2 of the last 52 weeks; the most was 94.9% of its area, on the October 21, 2025 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 0% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
3 flood losses since 2016, $82,748 paid. The worst year was 2025, with 1.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 1 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 39.38 in |
| 12 months to August 2026 | 40.32 in (+0.94) |
| 2025 | 33.43 in (-5.95) |
| Wettest year since 1895 | 2011: 54.15 in |
| Driest year since 1895 | 1934: 22.12 in |
| Days with 1 inch or more, normal at MARYSVILLE (9 mi away) | 9 |
Homes
| Housing units | 25,158 |
| Median year built | 1996 |
| Built before 1980 | 36% |
| Built 2000 or later | 44% |
| Owner-occupied | 79% |
| Median value, owner-occupied | $344,900 |
| Single-family detached | 80% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Cities in Union County
| City | Expansive clay | High water table | Homes |
|---|---|---|---|
| Magnetic Springs | 25% | 97% | 136 |
| Marysville | 24% | 83% | 10,472 |
| Milford Center | 39% | 93% | 270 |
| Richwood | 7% | 86% | 995 |
| Unionville Center | 16% | 50% | 64 |
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Delaware County, OH | 19 mi | 23% | 84% |
| Logan County, OH | 22 mi | 26% | 81% |
| Marion County, OH | 23 mi | 40% | 92% |
| Champaign County, OH | 24 mi | 13% | 83% |
| Madison County, OH | 28 mi | 36% | 94% |
| Franklin County, OH | 29 mi | 12% | 71% |
| Hardin County, OH | 30 mi | 35% | 97% |
| Morrow County, OH | 34 mi | 9% | 87% |
Sources: USDA SSURGO (September 8, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status