The Michigan State Park reservation site is very helpful.
Just keep in mind that a map provided of the state campground it will likely say that the map is not to scale.
That is because the campsites are wherever the trees ain't. So a roadway that looks to run in a perfectly straight line might actually be an "S" curve and sites that look to be right at the water's edge might be further away and even have no view of the lake at all.
No big deal, but I have avoided sites that I thought were too close together based on a map only to find out that this was not even remotely the case.