County · code 39159
Union CountyOhio
Union County is a county in Ohio with its seat in Marysville, formed in 1820.
- Founded1820
- County seatMarysville
- Land area432 sq mi + 5.1 sq mi water
- Population62,784 2020 Census
- Parcels mapped37,862 checked 15 October 2026
Where it is
Union 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 Delaware County, Franklin County, Logan County and Madison County
An old deed may name a county that no longer exists, or a boundary that has since moved.
Union County was created in 1820 from parts of Delaware, Franklin, Logan, and Madison counties.
- 1820Union County created Union created from Delaware, Franklin, Logan, Madison, Non-County Area 5 attached to Delaware, and Non-County Area 9 attached to Logan. · Ohio Laws 1819, 18th assy., loc., ch. 16, secs. 1, 8-9/pp. 56, 58; Chase, 3:ch. 428/p. 2133
- 1821Boundary clarified Boundary between Union and Madison was clarified (no change).with Madisonno change· Ohio Laws 1820, 19th assy., ch. 44/p. 73; Chase, 3:ch. 431/p. 2135
- 1824Boundary clarified Boundary between Union and Logan was clarified (no change).with Loganno change· Ohio Laws 1823, 22d assy., loc., ch. 5/p. 7; Chase, 3:ch. 438/p. 2136
- 1827Boundary clarified Boundary between Union and Madison was clarified (no change).with Madisonno change· Ohio Laws 1826, 25th assy., gen., p. 99; Chase, 3:ch. 457/pp. 2142-2143
Land and parcels
What the maps cover in Union
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 37,862 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 2 September 2026 · checked 15 October 2026 -
Address points Official
One point per address, 32,868 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
Union 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
Union 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 Union County.
See your own lot on these maps
Open Union 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 Union County
- When was Union County founded?
- Union County was founded in 1820, formed from Delaware County, Franklin County, Logan County and Madison County.
- What is the county seat of Union County?
- The county seat of Union County is Marysville.
- Is there an online parcel map for Union County?
- Yes. A public source publishes a parcel map of 37,862 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has Union County's boundary or name changed?
- Union County was created in 1820 from Delaware County, Franklin County, Logan County and Madison County. Its boundary has been clarified three times since, with no change on the ground.
- Is my lot in a flood zone?
- We do not have flood maps for Union County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby