Jefferson County is located in the northwestern part of New York. Jefferson County has a total area of approximately 1857 square miles of which 69% is land and 31% water. As of the census of 2000, there were 111,738 people, 40,068 households, and 28,127 families residing in Jefferson County, New York. The county is adjacent to the area where the Saint Lawrence River enters Lake Ontario. The Black River, which also empties into Lake Ontario, is an important stream in Jefferson County, NY. The county is named after Thomas Jefferson, the third president of the United States.