If you're interested in how the shape of Florida's counties, including Duval, have changed over time, we recommend the Atlas of Historical County Boundaries.
<2>
When there's a risk of an area code running out of phone numbers, an 'Overlay Area Code' is created that has the same geographic boundaries as the existing area code. In this case, the 904 code has been Overlayed with the 324 area code. New phone numbers in the Oak Haven area will be assigned with one of these codes: 904 or 324. As a result, placing a call in the Oak Haven area will require 10-digit dialing (where you enter both the area code and then the phone number).