Fort Casey is the most awesome campground in the state. The fort is super to explore (Kids love it!), the beach is a great place to walk and look for agates, the views are spectacular - there's a continuous parade of ship traffic coming into the sound, and there are plenty more places to explore on Whidbey Island. They have a great bus system that goes right by the park.
Vote: BEST Campground
2017 Pacific Northwest A-List: Important Dates