The state park is a multi use location. In addition to the campground with more than 450 sites there is an extensive day use area. Swimming, fishing, boating and a large function area is all available. Take US Route 1A until you see the sign for the reservation. The fee for non residents is $20 and $14 for residents, so unless you plan on making day of it, it can be quite expensive. Pay the fee at the pay station and then continue down to the day use area.
Picnic, swim and make a day of it.
Outside the reservation is the town with its attractions and free beach access.