List of New York counties:
- Albany County: formed in 1683 as one of the original 12 counties. County seat: Albany.
- Allegany County: formed in 1806 from part of Genesee County. County seat: Belmont.
- Bronx County: formed in 1914 from part of New York County that originally was in Westchester County. County seat: The Bronx. Coextensive with the Borough of The Bronx in New York City.
- Broome County: formed in 1806 from part of Tioga County. County seat: Binghamton.
- Cattaraugus County: formed in 1808 from part of Genesee County. County seat: Little Valley.
- Cayuga County: formed in 1799 from part of Onondaga County. County seat: Auburn.
- Chautauqua County: formed in 1808 from part of Genesee County. County seat: Mayville.
- Chemung County: formed in 1798 from part of Tioga County. County seat: Elmira.
- Chenango County: formed in 1798 from parts of Tioga County and Herkimer County. County seat: Norwich.
- Clinton County: formed in 1788 from part of Washington County. County seat: Plattsburgh.
- Columbia County: formed in 1786 from part of Albany County. County seat: Hudson.
- Cortland County: formed in 1808 from part of Onondaga County. County seat: Cortland.
- Delaware County: formed in 1797 from parts of Otsego County and Ulster County. County seat: Delhi.
- Dukes County: formed in 1683 as one of the original 12 counties. Transferred to Massachusetts in 1691.
- Dutchess County: formed in 1683 as one of the original 12 counties. County seat: Poughkeepsie
- Erie County: formed in 1821 from part of Niagara County. County seat: Buffalo.
- Essex County: formed in 1799 from part of Clinton County. County seat: Elizabethtown.
- Franklin County: formed in 1808 from part of Clinton County. County seat: Malone.
- Fulton County: formed in 1838 from part of Montgomery County. County seat: Johnstown.
- Genesee County: formed in 1802 from part of Ontario County. County seat: Batavia.
- Greene County: formed in 1800 from parts of Albany County and Ulster County. County seat: Catskill.
- Hamilton County: formed in 1816 from part of Montgomery County. County seat: Lake Pleasant.
- Herkimer County: formed in 1791 from part of Montgomery County. County seat: Herkimer.
- Jefferson County: formed in 1805 from part of Oneida County. County seat: Watertown.
- Kings County: formed in 1683 as one of the original 12 counties. County seat: Brooklyn. Coextensive with the borough of Brooklyn in New York City.
- Lewis County: formed in 1805 from part of Oneida County. County seat: Lowville.
- Livingston County: formed in 1821 from parts of Genesee County and Ontario County. County seat: Geneseo.
- Madison County: formed in 1806 from part of Chenango County. County seat: Wampsville.
- Monroe County: formed in 1821 from parts of Genesee County and Ontario County. County seat: Rochester.
- Montgomery County: formed in 1772 as Tryon County from part of Albany County. Renamed Montgomery County in 1784. County seat: Fonda.
- Nassau County: formed in 1899 from Queens County. County seat: Mineola.
- New York County: formed in 1683 as one of the original 12 counties. County seat: Manhattan. Coextensive with the Borough of Manhattan in New York City.
- Niagara County: formed in 1808 from part of Genesee County. County seat: Lockport.
- Oneida County: formed in 1798 from part of Herkimer County. County seat: Utica.
- Onondaga County: formed in 1792 from part of Herkimer County. County seat: Syracuse.
- Ontario County: formed in 1789 from part of Montgomery County. County seat: Canandaigua.
- Orange County: formed in 1683 as one of the original 12 counties. County seat: Goshen.
- Orleans County: formed in 1824 from part of Genesee County. County seat: Albion.
- Oswego County: formed in 1816 from parts of Otsego County and Onondaga County. County seat: Pulaski.
- Otsego County: formed in 1791 from part of Montgomery County. County seat: Cooperstown.
- Putnam County: formed in 1812 from part of Dutchess County. County seat: Carmel.
- Queens County: formed in 1683 as one of the original 12 counties. County seat: Jamaica. Coextensive with the Borough of Queens in New York City.
- Rensselaer County: formed in 1791 from part of Albany County. County seat: Troy.
- Richmond County: formed in 1683 as one of the original 12 counties. County seat: St. George. Coextensive with the borough of Richmond and with Staten Island in New York City.
- Rockland County: formed in 1798 from part of Orange County. County seat: New City.
- Saratoga County: formed in 1791 from part of Albany County. County seat: Ballston.
- Schenectady County: formed in 1809 from part of Albany County. County seat: Schenectady.
- Schoharie County: formed in 1795 from parts of Albany County and Otsego County. County seat: Ballston.
- Schuyler County: formed in 1795 from parts of Chemung County, Steuben County, and Tompkins County. County seat: Watkins Glen.
- Seneca County: formed in 1804 from part of Cayuga County. County seats: Ovid and Waterloo.
- St. Lawrence County: formed in 1802 from parts of Clinton County, Herkimer County, and Montgomery County. County seat: Canton.
- Steuben County: formed in 1796 from part of Ontario County. County seat: Bath.
- Suffolk County: formed in 1683 as one of the original 12 counties. County seat: Riverhead
- Sullivan County: formed in 1809 from part of Ulster County. County seat: Monticello.
- Tioga County: formed in 1791 from part of Montgomery County. County seat: Owego.
- Tompkins County: formed in 1817 from parts of Cayuga County and Seneca County. County seat: Ithaca.
- Ulster County: formed in 1683 as one of the original 12 counties. County seat: Kingston
- Warren County: formed in 1813 from part of Washington County. County seat: Lake George.
- Washington County: formed in 1772 as Charlotte County from part of Albany County. Renamed Washington County in 1784. County seat: Hudson Falls.
- Wayne County: formed in 1823 from parts of Ontario County and Seneca County. County seat: Lyons.
- Westchester County: formed in 1683 as one of the original 12 counties. County seat: White Plains
- Wyoming County: formed in 1841 from part of Genesee County. County seat: Warsaw.
- Yates County: formed in 1823 from parts of Ontario County and Steuben County. County seat: Pen Yann.