Tioga County /taɪˈoʊɡə/ is a county in the U.S. state of New York. As of the 2020 census, the population was 48,455. Its county seat is Owego. Tioga County is part of the Binghamton metropolitan area. The county is part of the Southern Tier region of the state.

The county's name is a corruption of Iroquois De-yoh-ho-gah, meaning "at the forks" or "where it forks."

In 1789, as the number of residents increased in the region, Montgomery County was reduced in size by the founding of Ontario County from some of its territory. The area taken from Montgomery County at that time was much larger than the present Ontario County, also including present-day Allegany, Cattaraugus, Chautauqua, Erie, Genesee, Livingston, Monroe, Niagara, Orleans, Steuben, Wyoming, Yates, and part of Schuyler and Wayne counties.

In 1791, Tioga County was founded by another division of territory from Montgomery County. At the time of its foundation, Tioga County included present-day Broome and Chemung counties and parts of Chenango and Schuyler counties.

Tioga County was reduced in size in 1798 by the splitting-off of Chemung County (which also included part of the present Schuyler County and by the combination of a portion with a portion of Herkimer County to create Chenango County. In 1806, it was further reduced by the splitting-off of Broome County.

According to the U.S. Census Bureau, the county has a total area of 523 square miles (1,350 km²), 519 square miles (1,340 km²) of which is land and 4.3 square miles (11 km²) (0.8%) of which is water.

Tioga County is in southwest New York State, west of Binghamton and directly north of the border with Pennsylvania. The Susquehanna River flows into Pennsylvania from this county. The county is considered part of the Southern Tier region of New York State.

The highest elevation is an unnamed 1,994-foot (608 m) hill in the county's northern corner. The lowest is 720 feet (220 m) on the state line where the Susquehanna flows into Pennsylvania.