We were there yesterday, campsites were plentiful. Be sure your car can handle the long climb up and your brakes are good for the trip back down. Enjoy!
I was there over the July 4 weekend. The road to deer park campground is closed to traffic. You may hike to the campground but I was told by the rangers at WIC that we need to get a back country camping pass since it's under Olympic national park and you need a permit for that. If it were a normal day, you could drive up there and that would be front country camping which is 'first come first stay' basis. I would give the WIC a call if I were you just to be at peace. It's just $8 per person.
I was just up there over the weekend and it was really empty. No reservation necessary
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