County · code 39147
Seneca CountyOhio
Seneca County is a county in Ohio with its seat in Tiffin, formed in 1820.
- Founded1820
- County seatTiffin
- Named forSeneca
- Land area551 sq mi + 1.8 sq mi water
- Population55,069 2020 Census
- Parcels mapped46,052 checked 14 October 2026
Where it is
Seneca on the map of Ohio
Ohio has 88 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Formed in 1820 from Huron County, Logan County and Sandusky County
An old deed may name a county that no longer exists, or a boundary that has since moved.
Seneca County was created in 1820 from parts of Huron, Logan, and Sandusky counties, but was not fully organized and remained attached to Sandusky for administrative and judicial purposes. In 1824, Seneca County was fully organized and detached from Sandusky, with part of Crawford County attached to it for judicial purposes. In 1826, Crawford County was fully organized and detached from Seneca County.
- 1820Seneca County created Seneca created from Non-County Area 8 attached to Huron and Non-County Area 9 attached to Logan; Seneca not fully organized, attached to Sandusky for administrative and judicial purposes. · Ohio Laws 1819, 18th assy., loc., ch. 37, secs. 1-2/pp. 91-92; Chase, 3:ch. 429/pp. 2134-2135
- 1824
- 1826Changed Crawford fully organized, detached from Seneca. · Ohio Laws 1825, 24th assy., gen., p. 46; Chase, 3:ch. 450/pp. 2140-2141
Land and parcels
What the maps cover in Seneca
Who publishes each layer, how good it is, and when we last checked.
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Parcels Good enough
Lot lines and tax-map numbers for 46,052 parcels from Seneca County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 13 October 2026 · checked 14 October 2026 -
Address points Official
One point per address, 25,765 in all from Ohio Geographically Referenced Information Program (OGRIP), Ohio DAS/OIT (state GIS office).
edited 24 June 2025 · checked 13 October 2026 -
Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
Seneca by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
Seneca County's official site
We have found the county's site but not its offices yet; start there.
County government
- County government
The official website of Seneca County.
See your own lot on these maps
Open Seneca County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about Seneca County
- When was Seneca County founded?
- Seneca County was founded in 1820, formed from Huron County, Logan County and Sandusky County, and named after Seneca.
- What is the county seat of Seneca County?
- The county seat of Seneca County is Tiffin.
- Is there an online parcel map for Seneca County?
- Yes. Seneca County publishes a parcel map of 46,052 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has Seneca County's boundary or name changed?
- Seneca County was created in 1820 from Huron County, Logan County and Sandusky County. Since then the Atlas of Historical County Boundaries records 2 later changes, chiefly involving Crawford County, Delaware County and Sandusky County.
- Is my lot in a flood zone?
- We do not have flood maps for Seneca County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby