Before 1772 Albany county covered all but the southeastern part of the State as then bounded, including Vermont. As substantial settlements developed along the Mohawk valley, the onerous tax imposed upon the people by their being compelled to go all the way to Albany to avail themselves of the courts created the need to divide the county. Sir William Johnson was the principal mover in the petition to create the new county. Tryon county was formed on July 30, 1772 from Albany county. Tryon county covered all of the State west of a line running due north from the Delaware river, through what is now Schoharie county, and along the eastern limits of the present counties of Montgomery, Fulton and Hamilton to the Canadian line. It was named for the governor of the colony, William Tryon, and the county seat was designated as Johnstown, Sir William Johnson's home.

There were about 10,000 residents, mostly settled along the Mohawk. Instead of townships, it was divided into five large districts. The most eastern district was called the Mohawk and consisted of a strip of the State between the east line of the county, already defined, and a parallel line crossing the Mohawk river at the "Noses" (a narrowing of the mountains along the Mohawk river valley). The Stone Arabia district extended indefinitely northward from the river, between the Mohawk district on the east and on the west a north and south line through the State, crossing the river at Little Falls. With the same breadth, the Canajoharie district reached southward to the Pennsylvania line. North of the Mohawk river and west of the Stone Arabia district, as far as settlements extended, was the Kingsland district, while south of the river, extending westward from the Canajoharie district to the meridian of Fort Stanwix (near Rome) and southerly to the Pennsylvania line, was the German Flats district. One year later the Stone Arabia district was changed to Palatine.

The county was renamed Montgomery county on April 2, 1784, after General Richard Montgomery. (From "History of Herkimer County, N.Y.," F. W. Beers & Co., 36 Vesey Street, New York, 1879)