A new area code was implemented in Western Washington in 2017.
The area code, 564, was created to assign as numbers in the 360, 206, 253, and 425 area codes become exhausted.
Part of this roll out included the implementation of mandatory 10-digit dialing for all western Washington area codes, which required callers to dial all 10 digits of a telephone number, including area code, when making local calls.
The 564 area code was distributed to new numbers in the 360 area code beginning August 2017.
The 425, 206, and 253 area codes are not exhausted and are still available for service providers to assign to customers. Once these codes are nearing exhaustion the 564 overlay will go into effect for those areas.
- North American Numbering Plan Administrator website.