I have never heard of dispersed camping before...only have camped at NFS campgrounds in several states where we made reservations. Exactly how does dispersed camping work?
The State forests here in PA, BLM land out West, Crown land in Canada and most, if not all, of the National Forests in the US allow dispersed, minimum impact camping outside of designated areas. This is on a "leave no trace" basis or, in the terminology of my childhood, we were told to "take only pictures and leave only footprints".
As it relates specifically to camping, there are seven keys to remember:
1) Any and all trash must be packed out.
2) Do not clear vegetation.
3) Camp at least 100 feet from any water source.
4) Dispose of any waste water at least 200 feet from any water source.
5) All human waste should be buried at least 6 inches deep and not less than 200 feet from a water source.
6) No standing trees (technically, not even the dead ones) should be cut and especially in heavily used areas,
7) All campsites should be a minimum of 25 feet off of the trail and, ideally, out of sight of the trail.
For my extended trips, I try to use only established sites (most of which ignore some of the above rules) but I've had to improvise at times and I take a bit of pride in looking over a site after packing and knowing that the average person would never suspect that anyone had stayed there.
Note: I believe that dispersed camping is allowed in Superior Nat'l Forest
except within the BWCA. There, it is restricted to designated sites only.
As always, it's best to check with the landowner (or, in this case, the land manager) before you go.