Stayed for three nights at the upper Fort Clinch sites, there are six tent sites and a good number of RV spots.
Check-in is 3 PM but the ranger station closes at 5 and gates lock shortly after. I called in advance and received a gate code. Ranger station only opens at 10:30 so I didn't see them for my entire stay, but very nice folks on the phone.
Tent sites provide water no power. RV sites are a mix, have to check individual site description. Free dump site.
Bathrooms are big, clean, with toilet paper and hand soap.. Showers are free and decent. Coin laundry available.
Tent site was relatively level, be careful to stay inside the "corral," I went out (but not past the protected area sign) and got bit by cacti.
Beach is lovely and quiet.
Heat index was over 100 so didn't do much hiking, but this was a really nice place to spend a few nights. I do wonder if the river campsites on the other side of the park might be cooler and offer hammock opportunities.
Park is huge, lots to explore when weather permits.
Lots of bugs but basic precautions handled it. There was also a turtle burrow behind the tent site, and saw a bunch of little deer!