Every park in which I've ever stayed, whether private or public, has different limits as befits their varied topography. They don't stamp out camp sites using a mold or die, they carve them out as fits the location, and what's more, it's perfectly legal to do that. Thus there is no answer to the question. Whatever rig you get will be too long for some sites and some campgrounds.
My TT is 21 feet, a length most here would classify as a shortie. And I recall staying one night in a KOA that squeezed me into the only available site, which was officially listed as 20 feet or shorter. I had to park my TV out in the parking lot after backing in to where my trailer was up against this fence at the back, and my hitch was right at the edge of the access road. Well, ok, it hung out about 6 inches.
I volunteer at an NFS campground most of which was built in the 1930s. One section is limited to a max of 28 feet, due to the access roads. In that section, there are sites that could accommodate 65 footers easily, if you could get one in there. There are also sites that can accommodate only a car-length, call it 15 feet.
YMMV.