When the colony that is now New York State established its first twelve counties in 1683, the present Sullivan County was part of Ulster County. In 1809, Sullivan County was split from Ulster County.
In the late 19th century, the Industrial Revolution and the advent of factories driven by water power along the streams and rivers led to an increase in population attracted to the jobs. Hamlets enlarged into towns. As industry restructured, many of those jobs left before the middle of the twentieth century.