Tioga County, New York: History
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.