Fort McCoy hosts several running trails that are open to the public. All are double track trail and most are sandy to some degree. Directly behind the ski hill is a trail with a fitness course on it if you're into that kind of thing. I stopped at the campgrounds and asked about running on the snowmobile trails and was told that it wouldn't be a problem as long as I stayed on public use lands. During the summer months you may want to start your run at the campgrounds as there is a swimming area there for when you finish your run.
As I've yet to run the same route twice I don't know how many miles of trails Fort McCoy has, I'm sure it is a bunch.
Fort McCoy is 21 miles from Norwalk.
Looking up from the bottom of the ski hill.
Looking down from the top of the ski hill.
Notice on the map there are no street names. The directions to both the ski area and campgrounds are clearly marked with big signs that can't be missed.