Jefferson County, New York
Jefferson County is a county in the U.S. state of New York. As of the 2010 census, the population was 116,229. Its county seat is Watertown. The county is named after Thomas Jefferson, third President of the United States of America. It is adjacent to Lake Ontario, southeast from the Canada–US border of Ontario.
When counties were established in the Province of New York in 1683, the present Jefferson County was part of Albany County. This was an enormous county, 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.