Deputy Jason Johnson says the truck driver, Robert Lange, of Kalispell, Mont., was a passenger on his way home when the bus crashed Sunday morning on an icy interstate highway near Clinton.
Johnson says the other victim, Fatimah Amatullah, of Chicago, was on her way to visit relatives in Seattle.
Lange, Amatullah and two others were pinned under the bus after it spun around and rolled onto its side.
All 32 others onboard the Billings-to-Missoula bus were injured. St. Patrick Hospital spokeswoman Joanne Hoven says one person is in critical condition and seven others are in serious condition.
