Area code 904 is in use for much of the First Coast region of the U.S. state of Florida, including all of the metropolitan area of Jacksonville. At its largest, it covered the entire northern half of Florida. It was split from area code 305 on Sunday July 11th, 1965, as a "flash-cut" with no formal permissive dialing period.
Area code splits in the 1990s resulted in schisms across much of north Florida (into area code 850, 352, and 386). Many new metropolitan areas in north Florida necessitated these new area codes. As well, there were a lack of unique phone numbers due to a plethora of new phone lines, especially in the expanding Jacksonville metro area.
