During busy times you do, but we went off season without a reservation and they let us stay.
During off season there is no reservation on any site. During season they have some with no reservation, the others are by reservation. If you just show up and the site is not resevered you can stay, but you night have to move if it is reserved the following day. I recommend that you check the site for if it is reserved before setting up. They do fill up fast so I do recommend setting up the reservation.
They do have a few first come first serve sites. Busy seasons definitely need reservations. On a personal note I'd never go to a State Park during peak season without one.
Off season no but would recommend it if it is during peak times. They fill up fast.
Reservations are not required, but recommended. Summer and weekends are the busiest of course, but there are often vacancies and cancelations.
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