When was Onondaga County founded?

Onondaga County was founded in 1794, formed from Herkimer County and Tioga County, and named after Onondaga.

What is the county seat of Onondaga County?

The county seat of Onondaga County is Syracuse.

Is there an online parcel map for Onondaga County?

Yes. New York State Geographic Information Systems (GIS) Clearinghouse publishes a parcel map of 181,909 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Onondaga County's boundary or name changed?

Onondaga County was created in 1794 from Herkimer County and Tioga County. Since then the Atlas of Historical County Boundaries records 4 later changes, chiefly involving Cayuga County, Cortland County and Oswego County.

Is my lot in a flood zone?

We do not have flood maps for Onondaga County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

County · code 36067

Onondaga CountyNew York

Onondaga County is a county in New York with its seat in Syracuse, formed on March 5, 1794.

Founded1794
County seatSyracuse
Named forOnondaga
Land area778 sq mi + 27 sq mi water
Population476,516 2020 Census
Parcels mapped181,909 checked 15 October 2026

Open the free map Click any parcel in Onondaga County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated 19 October 2026

Census outline · seat marked

History

Formed in 1794 from Herkimer County and Tioga County

An old deed may name a county that no longer exists, or a boundary that has since moved.

Onondaga County was created from Herkimer and Tioga on March 5, 1794, and named after the Onondaga people. It lost territory to the creation of Cayuga County in 1799, Cortland County in 1808, and Oswego County in 1816, and exchanged small areas with Cayuga County in 1828.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries.

1794
Onondaga County created Onondaga created from Herkimer and Tioga.
from Herkimer from Tioga
5 March 1794 · N.Y. Laws 1794, 17th sess., ch. 18/p. 491
1799
Lost territory Onondaga lost to creation of Cayuga.
to Cayuga
8 March 1799 · N.Y. Laws 1798-1799, 22d sess., ch. 26/p. 333
1808
Lost territory Onondaga lost to creation of Cortland.
to Cortland
8 April 1808 · N.Y. Laws 1808, 31st sess., ch. 194, sec. 1/p. 365
1816
Lost territory Onondaga lost to creation of Oswego.
to Oswego
1 March 1816 · N.Y. Laws 1816, 39th sess., ch. 22, sec. 1/p. 16
1828
Exchanged territory Onondaga exchanged small areas with Cayuga.
with Cayuga
15 April 1828 · N.Y. Rev. Stat., 3:14-15

Land and parcels

What the maps cover in Onondaga

Who publishes each layer, how good it is, and when we last checked.

Parcels Good enough

Lot lines and tax-map numbers for 181,909 parcels from New York State Geographic Information Systems (GIS) Clearinghouse. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 25 September 2026 · checked 15 October 2026
Address points Official

One point per address, 235,002 in all from NYS Office of Information Technology Services (ITS), Geospatial Services / GIS Program Office (AGOL org 'ShareGIS NY', owner NYSGIS_GPO).
edited 25 September 2026 · checked 14 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

Onondaga by the Census

Population

476,516 2020 Census count

Housing units

211,343 2020 Census count

Land area

778 square miles

Water area

27 square miles

People per sq mi

612 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

Onondaga 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 Onondaga County.
ongov.net

See your own lot on these maps

Open Onondaga 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.

Open the free map no sign-in Pro early access

Questions

Common questions about Onondaga County

When was Onondaga County founded?: Onondaga County was founded in 1794, formed from Herkimer County and Tioga County, and named after Onondaga.
What is the county seat of Onondaga County?: The county seat of Onondaga County is Syracuse.
Is there an online parcel map for Onondaga County?: Yes. New York State Geographic Information Systems (GIS) Clearinghouse publishes a parcel map of 181,909 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Onondaga County's boundary or name changed?: Onondaga County was created in 1794 from Herkimer County and Tioga County. Since then the Atlas of Historical County Boundaries records 4 later changes, chiefly involving Cayuga County, Cortland County and Oswego County.
Is my lot in a flood zone?: We do not have flood maps for Onondaga County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby