St Johns County is a county located in the U.S. state of Florida. The county seat is St. Augustine. It is one of the highest-income counties in the United States. St Johns County is part of the Greater Jacksonville Metropolitan area. St Johns County was created in 1821 and was named for St.John the Baptist. St Johns County has a total area of approximately 821 square miles of which 74% is land and 26% water. As of the 2000 census, there were 123,135 people, 49,614 households, and 34,084 families residing in St Johns County, FL.