If you are thinking about staying at any of the Oregon state Parks it is best to have a reservation for the coastal parks, yes even in September! There are a couple parks that are first come first severed they are a little south of central, Washburn is one can't recall the other.
It is currently the third week of October, and the numbers are finally getting smaller, and we have empty spaces, currently at South Beach SP.
Other than our favorite of the Oregon Coast, Mt Rainer, Crater Lake, The Olympic NP and Peninsula. I have discussed with DW of hosting in Central Washington to see the scars of the Glacial Lake Missoula. Grand Coulee dam and all the dams of the Columbia.
If you ever can stick to a schedule, make sure your are on Reserve America at 11:55 pm nine months before the date you will be at Beachside SP (just south of Waldport, OR and try for site #63! Site is about 40' and has Ocean exposure on two sides (door side and rear)! Good luck! If you can't get it try for sites #64, #66, #68, and #70 all have rear ocean exposure.
Beachside SP Map