Established in 1947, area code 504 was the sole area code allocated to Louisiana until 1957. In 1957, most of the state west of the
Mississippi River was reassigned with
area code 318. In 1998, the western portion of the numbering plan area, including
Baton Rouge, was renumbered with
area code 225 in an
area code split. In 2001, much of southeastern Louisiana was split off with
area code 985, to both the west and the north of 504. Several of New Orleans' downriver suburbs switched to 985 in 2001 as well. However, much of this area switched back to 504 in 2007. These communities are now being served with dialtone from telephone switching facilities in New Orleans following near-total destruction of local switching facilities due to flooding from
Hurricane Katrina. Permissive dialing of 504 alongside 985 in this area began on July 29, 2007. Mandatory use of 504 to again reach these communities began on May 1, 2008. These communities are on both sides of the Mississippi River in lower Plaquemines Parish, including
Pointe à la Hache on the east bank, with
Port Sulphur,
Buras, and
Boothville on the west bank. Prior to October 2021, area code 504 had telephone numbers assigned for the
central office code 988. In 2020,
988 was designated nationwide as a dialing code for the
National Suicide Prevention Lifeline, which created a conflict for exchanges that permit
seven-digit dialing. This area code was therefore scheduled to transition to
ten-digit dialing by October 24, 2021. ==Service area==