Group sites are booked further ahead than anything else — reunions, scout troops and weddings plan a year out — and there is rarely more than one or two per campground. A cancellation on a group site frees up a whole weekend for a whole party, which is why they do not sit unclaimed for long.
We track live availability at 1,320 campgrounds with group campsites across 31 states, on Recreation.gov and 13 state park systems. Every one is rechecked every 15 seconds, around the clock, so when a booked site frees up you hear about it in seconds rather than finding out weeks later that it was open for an hour.