Police said it was not clear if any suspects remained on the loose or were among the dead, and warned residents of the sparsely populated, wooded area near the town of Laurel to be careful.
"We have five dead people and we're trying to find out how they died," said Sgt. Jerry Goodin, spokesman for the Indiana State Police. "Some of the victims had gunshot wounds, or what appear to be gunshot wounds."
The Marion County coroner's office in Indianapolis was scheduled to perform autopsies Monday.
Police did not immediately release the identities of the victims, pending notification of family members. Goodwin said Sunday he did not know "if the shooter or shooters could be among the deceased."
A multi-agency investigation into the killings began after the Franklin County Sheriff's Department responded to a call Sunday afternoon about a child wandering along a road near Laurel, about 50 miles southeast of Indianapolis, according to a state police statement.
A deputy spoke with the child and neighbors, then called for backup to search the two homes. Police found a dead male inside a recreational vehicle and the bodies of two males and two females at the other home across the street. The statement didn't say if the dead were adults.
Goodin told The Associated Press that it was too early in the investigation to rule out the possibility that one or more suspects were on the loose and cautioned neighbors until that could be clarified.
"They should be vigilant," Goodin said. "They need to make sure they keep the doors locked. If they see any suspicious people, absolutely they should dial 911.