We live in GA and spend our summers in NJ. Our campground is more inland, about 15 miles from Philadelphia. It's not a tourist attraction - about 45 minutes to the closest NJ beach, but it is close to family which is why we are there. As our parents get older, they can't travel to see us anymore, so we spend the summers there so they can see their grand kids and we get a break from the relentless GA sun.
Our campground is pretty quiet during the week in the summer. It starts filling up Thursday and back to quiet Sunday evening. Holiday weekends are usually packed. Our campground doesn't allow pets, which probably keeps it from filling up all the time. Along the coast of NJ, campgrounds are usually close to full all summer long.
It would probably be beneficial to try a few different campgrounds for a summer or two to find one you like. Try to stay away from touristy areas to avoid the worst traffic and crowds. We lucked out and found our campground first try - although it wasn't hard since there are only 3 campgrounds in the County and the other 2 are a good bit further from family than we want to be.
-Michael