Eleven people were injured in the crash, which happened at about 4:30 p.m.
Indiana State Police Sgt. Rod Russell says some of the victims are believed to be from an Amish community near Fort Wayne, Indiana. Authorities say they are trying to verify whether there are also victims from other Amish communities in Indiana.
Amish people generally shun modern conveniences but sometimes enlist non-Amish as drivers.
At the scene, the van lay on its side with its roof gone. Traffic in both directions was stopped as authorities used the highway to land medical helicopters.
Seven such helicopters were called to the scene, said Bill Gosnell, director of the Delaware County Emergency Management Agency.
It was not clear at first how many people had been riding in the van, as survivors gave conflicting stories of 15, 16 or even 17 passengers. That led police and other responders to search for additional injured people until it became clear all people in the van were accounted for.
"It's controlled chaos, is what it is, when you have a situation like this," with ejections and many people injured, Russell said.
The crash occurred about 20 miles from the site of an April 2006 collision between a Taylor University van and a semi-trailer rig that killed four students and a university employee.
The crash resulted in a highly publicized case of mistaken identity after the family of a student believed dead turned out to be another girl originally thought to have survived the crash.
In April, four Amish riding in a pickup were among eight people killed in a crash on the Indiana Toll Road.
By Ken Kusmer