Start with King County if the death was in King County. Olympia (Washington State Department of Health) is the fallback for the rest of the state and for mail when the county counter is not practical.
Who may request
You must be a Washington qualified applicant. King County lists spouse or domestic partner and the other relationships on its order page. The state DOH page has the full qualified-applicant list. Noncertified informational copies may be requested without that relationship. Banks want a certified copy.
What to bring
One government-issued photo ID with full name and date of birth, not expired more than 60 days, plus one proof-of-eligibility document from the state DOH lists. Confirm both lists on kingcounty.gov and doh.wa.gov before you go.
Where to write or visit
Order through the King County death-certificate page. In-person kiosks use VitalChek. The Washington State Department of Health in Olympia is the statewide backup.
Notes from the desk
Each certified copy is $25. Additional copies are also $25 on the county page this check. Kiosks and online orders add VitalChek processing. That is not the state copy fee. This desk takes no cut. Order extras on the first request.