Seneca County, Ohio
A county in Ohio, ranked 47 of 88 by population.
CountyFIPS 39147
- Population
- 54,522
- -539 (-1.0%) since 2020
- Land area
- 551
- square miles. A further 0.3% of the total area is water
- Population density
- 98.9
- people per square mile, computed rather than published
- County seat
- Tiffin
- Seat of county government.
- Established
- 1820
- 205 years ago
- Largest city
- Tiffin city
- Population 17,803.
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.
Satellite view
Aerial imagery of Seneca County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.
Where Seneca County ranks
Position among the 88 counties of Ohio, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.
| Measure | Value | In Ohio | Nationally |
|---|---|---|---|
| Population | 54,522 | 47th of 88 | 954th of 3,144 |
| Land area | 551 sq mi | 16th of 88 | 1,897th of 3,144 |
| Population density | 98.9 per sq mi | 56th of 88 | 928th of 3,144 |
| Median household income | $66,025 | 48th of 88 | 1,539th of 3,143 |
Full data for Seneca County
| Measure | Value | Source and vintage |
|---|---|---|
| Population | 54,522 | Vintage 2025 Population Estimates |
| Population in 2020 | 55,061 | Vintage 2025 Population Estimates |
| 2020 estimates base? | 55,080 | Vintage 2025 Population Estimates |
| Land area | 551 sq mi | 2025 Gazetteer Files |
| Water area | 1.8 sq mi | 2025 Gazetteer Files |
| Total area | 552.8 sq mi | 2025 Gazetteer Files |
| Population density? | 98.9 per sq mi | Computed: Vintage 2025 estimates divided by 2025 Gazetteer land area |
| Median household income | $66,025 | American Community Survey 2020-2024 5-Year Estimates |
| Median home value | $154,700 | American Community Survey 2020-2024 5-Year Estimates |
| Median age | 40.2 | American Community Survey 2020-2024 5-Year Estimates |
| Households | 22,279 | American Community Survey 2020-2024 5-Year Estimates |
| Housing units | 23,982 | American Community Survey 2020-2024 5-Year Estimates |
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.
How the population changed
The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:
- Births minus deaths
- -89
- 560 births, 649 deaths
- Net migration
- -86
- More people moved out than moved in.
Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.
The 6 areas bordering Seneca County
Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.
| Bordering area | State | Shared border | Population |
|---|---|---|---|
| Sandusky County | Ohio | 30 mi | 58,655 |
| Huron County | Ohio | 18 mi | 58,250 |
| Wyandot County | Ohio | 16 mi | 21,567 |
| Crawford County | Ohio | 15 mi | 41,896 |
| Hancock County | Ohio | 12 mi | 75,034 |
| Wood County | Ohio | 6.0 mi | 134,176 |
Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.
All 88 counties of Ohio
Open the interactive Ohio county map, or jump straight to any of them.
- Adams County
- Allen County
- Ashland County
- Ashtabula County
- Athens County
- Auglaize County
- Belmont County
- Brown County
- Butler County
- Carroll County
- Champaign County
- Clark County
- Clermont County
- Clinton County
- Columbiana County
- Coshocton County
- Crawford County
- Cuyahoga County
- Darke County
- Defiance County
- Delaware County
- Erie County
- Fairfield County
- Fayette County
- Franklin County
- Fulton County
- Gallia County
- Geauga County
- Greene County
- Guernsey County
- Hamilton County
- Hancock County
- Hardin County
- Harrison County
- Henry County
- Highland County
- Hocking County
- Holmes County
- Huron County
- Jackson County
- Jefferson County
- Knox County
- Lake County
- Lawrence County
- Licking County
- Logan County
- Lorain County
- Lucas County
- Madison County
- Mahoning County
- Marion County
- Medina County
- Meigs County
- Mercer County
- Miami County
- Monroe County
- Montgomery County
- Morgan County
- Morrow County
- Muskingum County
- Noble County
- Ottawa County
- Paulding County
- Perry County
- Pickaway County
- Pike County
- Portage County
- Preble County
- Putnam County
- Richland County
- Ross County
- Sandusky County
- Scioto County
- Seneca County
- Shelby County
- Stark County
- Summit County
- Trumbull County
- Tuscarawas County
- Union County
- Van Wert County
- Vinton County
- Warren County
- Washington County
- Wayne County
- Williams County
- Wood County
- Wyandot County
Data on this page last rebuilt 30 August 2026. How these figures are produced.