Just do a simple Google Search. Type in the name of a city, state and the word Campground, and you'll get a list as long as your arm.
Out of curiosity, I just typed in Phoenix, Arizona. Up popped a bunch of hits and a map on the right side of the page. Identified on the map are:
Pleasant Harbor RV Resort
Riverside Campground
Well, shoot! There's too many.
Just
click here and you'll see what I mean.
Then you can click on any of the links and get more info. It's faster and easier than fumbling through lists on pages in small print that takes a microscope to read with.
Search by "State Park" or "Private Campground" or even "Boondock" or "RV Resort" and the lists are almost endless.