Boondocking is what we have always done
Being new to owning a travel trailer hearing people talk about Boondocking seems odd to us because that is really all we have ever done. First tents, then a pop-up but always in an area where the only utility was a hand water pump, which sometimes was a few miles from where we camped.
But to answer your question, here in WV the national forests have campgrounds and they are boondocking sites. Some are close to other sites; maybe a dozen in one area but others you may be the only site for a half mile or mile. Many of the state parks here have sites that you can choose; electric, elec. and water or nothing.