Otsego County is a county in the U.S. state of New York. As of the 2020 census, the population was 58,524. The county seat is Cooperstown. The county's population center is Oneonta. The name Otsego is from a Mohawk or Oneida word meaning "place of the rock." The county is part of the Mohawk Valley region of the state.

In 1789, Ontario County was split off from Montgomery. The area split off from Montgomery County was much larger than the present county, as it included the present Allegany, Cattaraugus, Chautauqua, Erie, Genesee, Livingston, Monroe, Niagara, Orleans, Steuben, Wyoming, Yates, and part of Schuyler and Wayne counties.

Otsego County was one of three early counties split off from Montgomery (the other two being Herkimer and Tioga) after the American Revolutionary War. Otsego County was officially established on February 16, 1791, with Cooperstown as its county seat. The original county consisted of three large townships:

Otsego and Cherry Valley together roughly covered the area of modern Otsego County, while Harpersfield covered the area south of the current county as far as the Delaware River.

Governor George Clinton made the original appointments to Otsego County government positions, including:

By 1793, four towns had been added to the county by division of the existing towns:

In 1795, a piece of Otsego County was joined with a portion taken from Albany County to create Schoharie County.

In 1797, a piece of Otsego County was joined with a portion taken from Ulster County to create Delaware County.