KOA was recommended to me by a Glacier friend:
http://koa.com/campgrounds/st-mary/
That link is for the campground map. Section K and L are tent sites. I was in L23 last year. L25 is the primo site in that section. Close to river and at the end of the road. Lots of shade and trees. Its a real nice site. Depending on time of year, I'm sure there are skeeters though.
Koa has much nicer facilities as well. Nice hottub and showers. Very nice laundry and small store.
I dunnno why everyone thinks Johnsons is better unless it's because they know the owners maybe?