Area code 623  was created in a split from area code 602 on April 1, 1999, when it was deemed that the Greater Phoenix metropolitan area could no longer continue with just one area code due to the explosive growth of the Phoenix metropolitan area in the 1990s.  The western suburbs and the city west of 39th Ave North of Indian School to west of 63rd Ave from I-10 south became Area code 623, along with the city from North of Union Hills and west of the 2000 E Grid.

Area Code 623:

City	County
ARIZONA STATE UNIV WEST	Maricopa County
ARLINGTON	Maricopa County
AVONDALE	Maricopa County
AVONDALE-GOODYEAR	Maricopa County
BUCKEYE	Maricopa County
CASHION	Maricopa County
EL MIRAGE	Maricopa County
GILA BEND AF AUX FIELD	Maricopa County
GLENDALE	Maricopa County
GOODYEAR	Maricopa County
LITCHFIELD PARK	Maricopa County
LUKE AFB	Maricopa County
NEW RIVER	Maricopa County
PALO VERDE	Maricopa County
PEORIA	Maricopa County
PHOENIX	Maricopa County
SUN CITY	Maricopa County
SUN CITY WEST	Maricopa County
SURPRISE	Maricopa County
TOLLESON	Maricopa County
TONOPAH	Maricopa County
WADDELL	Maricopa County
YOUNGTOWN	Maricopa County