Just before the campground there is a dirt road that has tons of free BLM camping.
There are a bunch of campsites on the road to the right, just before the bridge.
Mill Hollow turns into basically a mud pond in the summer when the water gets low.
Butterfly lake gets a lot of day use traffic since it is right off of Mirror Lake highway. It really quiets down in the evening though and the sun reflects on Hayden Peak.