Officials say the girl, whose name was not released, was driving the ATV near a Hinsdale campground just before 3 p.m. Saturday when she was hit by a motorcycle at a trail intersection. The motorcycle was operated by 52-year-old Michael Binney, of East Longmeadow, Mass.
A preliminary investigation found the front wheel of the motorcycle hit the girl.
Binney refused medical treatment.
The girl was taken to Brattleboro Memorial Hospital and later airlifted to Dartmouth Hitchcock Medical Center in Lebanon, N.H.
An investigation into the crash is continuing.