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County · code 36069

Ontario CountyNew York

Ontario County is located in New York and was created in 1789 from Montgomery County, with its county seat at Canandaigua. The county was named after Lake Ontario.

  • Founded1789
  • County seatCanandaigua
  • Named forLake Ontario, North America
  • Land area644 sq mi + 18 sq mi water
  • Population112,458 2020 Census
  • Parcels mapped51,318 checked 15 October 2026
Open the free map Click any parcel in Ontario County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

YatesSenecaLivingstonWayneSteubenMonroe Canandaigua Census outline · seat marked

Where it is

Ontario on the map of New York

New York has 62 counties and county equivalents, each with its own records office. Shapes with a page are links.

Albany CountyAllegany CountyBronx CountyBroome CountyCattaraugus CountyCayuga CountyChautauqua CountyChemung CountyChenango CountyClinton CountyColumbia CountyCortland CountyDelaware CountyDutchess CountyErie CountyEssex CountyFranklin CountyFulton CountyGenesee CountyGreene CountyHamilton CountyHerkimer CountyJefferson CountyKings CountyLewis CountyLivingston CountyMadison CountyMonroe CountyMontgomery CountyNassau CountyNew York CountyNiagara CountyOneida CountyOnondaga CountyOrange CountyOrleans CountyOswego CountyOtsego CountyPutnam CountyQueens CountyRensselaer CountyRichmond CountyRockland CountySt. Lawrence CountySaratoga CountySchenectady CountySchoharie CountySchuyler CountySeneca CountySteuben CountySuffolk CountySullivan CountyTioga CountyTompkins CountyUlster CountyWarren CountyWashington CountyWayne CountyWestchester CountyWyoming CountyYates CountyOntario County Ontario
Counties of New York · Ontario highlighted

History

Formed in 1789 from Montgomery County

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

Ontario was created from Montgomery County on January 27, 1789. Over its early decades, Ontario's boundaries changed significantly: it lost territory to the creation of Steuben, Genesee, Livingston, Monroe, Yates, Wayne, and Seneca counties, while also exchanging and gaining land with Cayuga and Steuben counties.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

  1. 1789
    Ontario County created Ontario created from Montgomery.
    from Montgomery
    · N.Y. Laws 1789, 12th sess., ch. 11/p. 10
  2. 1796
    Lost territory Ontario lost to creation of Steuben.
    to Steuben
    · N.Y. Laws 1796, 19th sess., ch. 29/p. 667
  3. 1801
    Exchanged territory Ontario exchanged with Cayuga.
    with Cayuga
    · N.Y. Laws 1801, 24th sess., ch. 123/p. 290
  4. 1802
    Lost territory Ontario lost to creation of Genesee; Genessee not fully organized, attached to Ontario for administrative and judicial purposes.
    to Geneseeto Genessee
    · N.Y. Laws 1802, 25th sess., ch. 64/p. 97
  5. 1804
    Gained territory Ontario gained from Cayuga.
    from Cayuga
    · N.Y. Laws 1804, 27th sess., ch. 31/p. 112
Show all 13 changes (8 more)
  1. 1789
    Ontario County created Ontario created from Montgomery.
    from Montgomery
    · N.Y. Laws 1789, 12th sess., ch. 11/p. 10
  2. 1796
    Lost territory Ontario lost to creation of Steuben.
    to Steuben
    · N.Y. Laws 1796, 19th sess., ch. 29/p. 667
  3. 1801
    Exchanged territory Ontario exchanged with Cayuga.
    with Cayuga
    · N.Y. Laws 1801, 24th sess., ch. 123/p. 290
  4. 1802
    Lost territory Ontario lost to creation of Genesee; Genessee not fully organized, attached to Ontario for administrative and judicial purposes.
    to Geneseeto Genessee
    · N.Y. Laws 1802, 25th sess., ch. 64/p. 97
  5. 1803
    Changed In March 1803, Genesee was fully organized, detached from Ontario.
    Genesee
    · N.Y. Laws 1802, 25th sess., ch. 64/p. 97
  6. 1804
    Gained territory Ontario gained from Cayuga.
    from Cayuga
    · N.Y. Laws 1804, 27th sess., ch. 31/p. 112
  7. 1814
    Gained territory Ontario gained from Steuben.
    from Steuben
    · N.Y. Laws 1814, 37th sess., ch. 24/p. 27
  8. 1821
    Lost territory Ontario lost to creation of Livingston and Monroe.
    to Livingstonto Monroe
    · N.Y. Laws 1820, 44th sess., ch. 57, sec. 1/p. 46; ch. 58, sec. 1/p. 50
  9. 1823
    Lost territory Ontario lost to creation of Yates.
    to Yates
    · N.Y. Laws 1823, 46th sess., ch. 30, sec. 1/p. 21
  10. 1823
    Lost territory Ontario lost to creation of Wayne.
    to Wayne
    · N.Y. Laws 1823, 46th sess., ch. 138, sec. 1/p. 158
  11. 1828
    Lost territory Ontario lost to Seneca.
    to Seneca
    · N.Y. Rev. Stat., 3:14-15
  12. 1860
    Changed Legislature authorized Ontario to gain from Yates, but change never took effect.
    Yates
    · N.Y. Laws 1860, 83d sess., ch. 76/p. 120
  13. 1922
    Lost territory Ontario lost small area to Livingston.
    to Livingston
    · N.Y. Laws 1922, 145th sess., ch. 258, secs. 1-2/p. 615

Land and parcels

What the maps cover in Ontario

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

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

Ontario by the Census

Population
112,458 2020 Census count
Housing units
52,585 2020 Census count
Land area
644 square miles
Water area
18 square miles
People per sq mi
175 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

Ontario County's official site

We have found the county's site but not its offices yet; start there.

County government

See your own lot on these maps

Open Ontario 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.

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Questions

Common questions about Ontario County

When was Ontario County founded?
Ontario County was founded in 1789, formed from Montgomery County, and named after Lake Ontario, North America.
What is the county seat of Ontario County?
The county seat of Ontario County is Canandaigua.
Is there an online parcel map for Ontario County?
Yes. New York State Geographic Information Systems (GIS) Clearinghouse publishes a parcel map of 51,318 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Ontario County's boundary or name changed?
Ontario County was created in 1789 from Montgomery County. Since then the Atlas of Historical County Boundaries records 12 later changes, chiefly involving Cayuga County, Genesee County and Livingston County.
Is my lot in a flood zone?
We do not have flood maps for Ontario County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby

Counties next door