The Butte KOA is off I-90’s exit 126, two blocks north (406/782-0063).
Farther from town, find the Forest Service’s (406/494-2147, www.fs.fed.us/r1/b-d [1]) Lowland campground to the north of town (Elk Park exit from I-15).
The Bureau of Land Management (406/533-7600, www.mt.blm.gov/bdo [2]) runs Divide Bridge and Dickey campgrounds south of town (Divide exit from I-15).
Links:
[1] http://www.fs.fed.us/r1/b-d
[2] http://www.mt.blm.gov/bdo