We are not lawyers and this is not official legal advice, this is simply our lived experiences navigating the legal system as trans people.
You must file for name change in the county of which your permanent address is. The current Fee: $301.50 ($83 filing fee, $10 administrative cost, $203.50 recording fee, $5 per certified copy). Make sure you sign the Petition for Name Change with CURRENT LEGAL NAME or it will be rejected. The Petition No. (in top right corner) will be filled in at time of filing the petition by the clerk, so don't worry about that. If you're filling out petition for waiver of court fees (MOTION AND DECLARATION FOR WAIVER OF CIVIL FEES AND SURCHARGES) for a name change, under section 1.2 write “PETITION FOR NAME CHANGE (Individual)." You will receive a court date via mail or email, BE THERE. The Judge will ask you some questions, such as if you are changing your name for fraud, and why you are getting a name change. Saying you are changing your name to match your identity or because you dislike your old name is legally valid, it is up to you if you would like to disclose your trans status.
Find more info here kingcounty.gov/courts/district-court/name-changes
Once your name change goes through, make sure you change ALL appropriate legal accounts and documents (you might need a certified copy for each of these). Remember: to change your birth certificate you have to follow the laws of where you were born/where your original birth certificate was issued, so laws may vary from WA laws. Here is a checklist to make sure you don’t have any trouble down the line (https://transequality.org/sites/default/files/docs/resources/ID-Documents-Overview.pdf)
Changing Gender marker on Drivers License/ID can be done at any DMV, ID Centers by filling out https://www.dol.wa.gov/forms/520043.pdf - Change of Gender Designation Form
To change your sex designation on your birth certificate (and in turn most other places), follow the steps listed below. Remember, that if you choose to legally change your sex designation, there is a chance of having troubles with insurance or getting the selective service to leave you alone in the future.
The 422-143-Request to Change Sex Designation on a Birth Certificate for an Adult form must be completed to request the birth certificate change
Make sure that it is signed in the presence of a Notary Public (these are at UPS offices)
If your full current legal name is different from what's on your birth certificate, provide a certified copy of the court order. If you want your name amended on your birth certificate, check the appropriate box on the form (they might ask for more documentation then).
Once your birth certificate sex designation change goes through, make sure you change ALL appropriate legal accounts and documents (you might need a certified copy for each of these). Remember: to change your birth certificate you have to follow the laws of where you were born/where your original birth certificate was issued, so laws may vary from WA laws. Here is a checklist to make sure you don’t have any trouble down the line: (https://transequality.org/sites/default/files/docs/resources/ID-Documents-Overview.pdf)
In order to amend a birth certificate (changing name or sex marker), you must go through the laws of the state you were born/have your original birth certificate with. Procedures vary depending on the state, some states will NOT issue a new/amended birth certificate, so look into the specific states.
Here is a good resource for looking at the different laws and procedures for each state for amending birth certificates: