Physical Characteristics. Duval County is in northeast Florida and is bordered by the Atlantic Ocean and Nassau, Baker, Clay, and St. Johns counties. The county has 776.49 square miles of land and 74.30 square miles of water for a total of 850.79 square miles. The average January temperature is 55.2 degrees Fahrenheit, and the average August temperature is 81.4 degrees Fahrenheit. The average annual rainfall is 58.20 inches.
History. Duval County was established in 1822 from St. Johns County and was named for William Pope Duval, first territorial governor of Florida. Jacksonville was nearly destroyed by fire in 1901. One of the largest ports in the state, Jacksonville developed a substantial shipbuilding industry during World War II.
