Physical Characteristics. Clay County is in northeast Florida and is bordered by St. Johns, Duval, Baker, Bradford, and Putnam counties. The county has 592.20 square miles of land and 51 square miles of water for a total of 643.20 square miles. The average January temperature is 55.4 degrees Fahrenheit, and the average August temperature is 81.3 degrees Fahrenheit. The average annual rainfall is 53.42 inches.
History. Clay County was established in 1858 from a portion of Duval County and named for Kentuckian Henry Clay, Secretary of State under John Quincy Adams. In the late 1800s the St. Johns River and Green Cove Springs were popular tourist spots.
