47°36′35″N 122°19′59″W / 47.60972°N 122.33306°W
Area code 564 is a telephone overlay area code in the North American Numbering Plan (NANP) for Western Washington state, including metropolitan Seattle. It overlays the combined numbering plan areas of area codes 206 and 360,
The area code was first proposed in 1999 to relieve telephone number shortages of area code 360, but implementation was delayed until 2017, when it was installed as an overlay to numbering plan area (NPA) 360. Neighboring area codes 206, 253, and 425 were slated for expansion of the overlay complex upon exhaustion of central office codes in each NPA. In 2023, area code 206 was approved for expansion with a guide line for preparation of inclusion of at least nine months.[1] Ten-digit dialing has been mandatory in all of western Washington since July 29, 2017.