You can probably get a start by clicking the "STATES" link on this website and get a summary of Washington laws. But I'd go to the King County site to get the latest details and see what resources are available. They're the ones you'll ultimately have to deal with.
If you're military and stationed in a different state you may be able to file where you're stationed rather than Washington (civilians typically don't have this option). That may be more convenient for you, and the divorce laws may be more advantageous to one or both of you in terms of grounds, waiting period, how property division, spousal support and child custody are handled. So I'd check that too if I were in your shoes.