Are there any first come first serve campsites

You want to make a reservation. This is a very popular park.

You most definitely must make a reservation about a year out especially if you want space 15

At Clackamette park

The weekends you will want to make reservations especially in July and August. During the week there is typically spaces available. If you want specific spots like 40 or 15 you would want to make reservations.