Area codes 904 and 324 are telephone area codes in the North American Numbering Plan for most of the First Coast (northeast) region of the U.S. state of Florida. The numbering plan area comprises most of the metropolitan area of Jacksonville. It includes all of Duval County, St. Johns County, Nassau County, and Baker County, and almost all of Clay County. Area code 904 was created in an area code split of area code 305 in 1965. In 2024, the numbering plan received a second area code, 324, through the creation of an overlay complex to mitigate central office code exhaustion and provide additional telephone numbers in the area.