Essex County, New York: History
When counties were established in the state of New York in 1683, the present Essex County was part of Albany County. This was an enormous area, including the northern part of New York state as well as all of the present state of Vermont and, in theory, extending westward to the Pacific Ocean. This county was reduced in size on July 3, 1766, by the creation of Cumberland County, and further on March 16, 1770, by the creation of Gloucester County, both containing territory now in Vermont. On March 12, 1772, what was left of Albany County was split into three parts, one remaining under the name Albany County. One of the other pieces, Charlotte County, contained the eastern portion. On May 24, 1915, land was swapped between Essex and Hamilton counties, with Essex ceding Indian Lake for Fishing Brook Mountain. Hamilton gained an additional 20 square miles (52 km2), whereas Essex County lost 30 square miles (78 km2). This left Essex with its present size of 1,916 square miles (5,000 km2).
In 1784, the name "Charlotte County" was changed to Washington County to honor George Washington, the American Revolutionary War general and later President of the United States of America.
In 1788, Clinton County was split off from Washington County. This was a much larger area than the present Clinton County, including several other counties or county parts of the present New York state (near Clunes).
Essex County was split from Clinton County in 1799.