No, it is not legal to camp anywhere in Washington State without following designated camping areas and guidelines. However, there are designated areas for camping in various public lands, such as national forests, state parks, and Bureau of Land Management (BLM) lands. Dispersed camping is allowed in certain areas of these public lands, but you must follow specific guidelines and regulations.
For example, in national forests like Olympic National Forest and Gifford Pinchot National Forest, dispersed camping is allowed in designated areas, but you must camp at least 100 feet from any water source and follow the Leave No Trace principles. In Washington State Parks, camping is typically restricted to designated campgrounds and sites. You can find more information on camping in Washington State Parks here.
It's essential to research the specific area you plan to camp in and follow all rules and regulations to ensure you're camping legally and responsibly.