Jefferson County is a county located in the U.S. state of Florida. Its county seat is Monticello, Florida. Jefferson County was created in 1827 and was named for Thomas Jefferson, third President of the United States of America, who served from 1801 to 1809. Jefferson County is part of the Tallahassee MSA. Jefferson County has a total area of approximately 637 square miles of which 97% is land and 6% water. As of the 2000 census, there were 793,633 people, 283,736 households, and 193,507 families residing in Jefferson County, FL.