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.

[5] Tioga County is in southwest New York State, west of Binghamton and directly north of the border with Pennsylvania.

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.

As of the census of 2010, there were 51,125 people living in the county, with 22,203 housing units, of these 20,350 (91.3%) occupied, 1,853 (8.3%) vacant.

16.6% were of German, 16.4% English, 14% Irish, 9.6% Italian, 5% Polish and 4% Dutch ancestry according to Census 2000.

22.40% of all households were made up of individuals, and 9.40% had someone living alone who was 65 years of age or older.