This is a more complicated question than it sounds like, involving issues of both jurisdiction and venue. The first question is: can I file in Washington? That is a jurisdictional question, i.e. does the state of Washington have any authority in the case.
To start with, the divorce statutes require that at least one of the parties be a resident of the State of Washington at the time of the initial filing. There is no time period to establish residency under Washington law, so you do not have to have lived here for 6 months or a year like some other states require. However, residency does require living here with the intent to remain here; i.e. it is more than just a visit.
However, even if you live here, there is still the question of whether the state has jurisdiction over your spouse. Without that, the court might be able to grant a divorce, but not to enter orders that affect the other spouse, such as dividing property, ordering support, or entering a parenting plan. To have jurisdiction over the spouse, you either need their consent to jurisdiction, or for them to have resided in Washington at some point during the marriage (again, not just visited), or for the two of you to have conceived a child in the Washington. Also, there are some special rules for serving in the military in the state. If you can’t get jurisdiction over the spouse, you may need to file in the state the spouse is living in in order to enter meaningful orders.
There is also the issue of having jurisdiction as to children. As a general rule, the court may not have authority to enter orders related to children (such as a parenting plan) if the children have not lived in the state for at least 6 months.
Now comes venue. Assuming the state has jurisdiction, venue deals with which court in the state to file in. All divorce actions are handled through the Washington Superior Courts – the issue is which county. You can actually file in any county in Washington as long as the other party agrees. Without the other party’s agreement, venue is proper in a county either party resides in. For instance, if you live in King County and your spouse lives in Snohomish, you could file in either of those counties. But if you filed in Pierce, your spouse would be able to challenge the venue there and have the case moved to either King or Snohomish.
If you are encountering any of these issues, please see an attorney for advise about your particular circumstances.