I've camped in both states during June & July without reservations. While there were times I was unable to get into some of Oregon's coastal state parks, I always found a commercial park near by. Going inland opens up many more locations. State parks such as
Collier Memorial or
Joseph H Stewart are likely to have openings since they have some non reservable sites. I've stayed at
Susan Creek BLM campground to explore the waterfalls along Oregon Route 138; one of my favorites.
As long as you have some flexibility in your plans, I don't feel you need reservations - I rarely make them other than holiday weekends in popular areas...
