The Lake County Sheriff's Office in Indiana said the crash happened just before 8:30 a.m. in the 3300-block of West 133rd Avenue in unincorporated Crown Point.
A preliminary investigation shows a Crown Point school bus was traveling westbound on 133rd Avenue when it veered off the road to the north, struck a mailbox and overcorrected to the left of the center of the road and into the path of oncoming traffic, the sheriff's office said.
Investigators believe the driver of a Ford Edge SUV tried to avoid crashing but collided with the bus head-on.
The SUV's driver, a 53-year-old woman, was transported to a local hospital in critical condition, but later died. The medical examiner's office later identified her as Lisa Smith.
The bus driver was transported to a local medical facility for evaluation. The bus monitor was released from the scene.
The sheriff's office said the bus driver and bus monitor were the only people on the bus at the time of the crash. There were no students onboard.
The Lake County Sheriff's Department Traffic Unit is investigating the crash.