Amber Stanley, 24, and her two children Jack (4) and Autumn (2) from Callahan, Florida, all died as a result of the crash.
Kyle Jacob Frank, 21, of Spring Hill, died at Trinity Medical Center, where he was taken after the single-vehicle crash.
According to the Montana Highway Patrol, the crash was reported at 3:39 a.m. Monday.
Troopers say the driver of a 2011 Kia Soul struck an animal that was in the road near the 86 mile marker.
Miraculous recovery for boy with severe brain trauma
His mum, Jennifer Reindl, instructed FOX10: "All I noticed was a stretcher together with his toes hanging out". According to Trenton's mother Jennifer Reindl, via Fox 10 , the doctors said her son was unlikely to recover.
He says the vehicle then ran off the left side of the road, into the median, before it struck a tree and caught fire.
According to the release, Robert R. Simpson, 29, of McDermott was traveling south on State Route 104.
The cause of the crash is still being investigated.