Washington Department of Health (USA)

On January 4, the Washington Department of Health announced a new rule allowing state residents who “don’t identify as male or female” to “choose X as their gender on birth certificates” starting January 27. The policy applies only to altering existing documents; it does not apply to new documents.
The Washington Department of Health defines “X” as: “A gender that is not exclusively male or female, including, but not limited to, intersex, agender, amalgagender, androgynous, bigender, demigender, female-to-male, genderfluid, genderqueer, male-to-female, neutrois, nonbinary, pangender, third sex, transgender, transsexual, Two Spirit, and unspecified.”
Washington is the the fourth jurisdiction, following California, Oregon, and the District of Columbia, to allow individuals to “legally recognize a nonbinary gender.”

Washington state offers third gender option on birth certificates — CNN

Washington State Adds Third Gender Option On Birth Certificates — NewNowNext