The family of five found murdered in their Beason home this week died from blunt force trauma, police said.
Police would not speculate on which object or weapon was used in the murder.
The only survivor of the crime, a three-year-old child, remains in critical but stable condition.
"We expect her to continue to recover," said Logan County Sheriff Steven Nichols.
In response to the crimes, Logan County police have formed a task force consisting of the Illinois State Police, Lincoln County police, the FBI, and the Logan County State Attorney's office.
Authorities continue to search for a Ford Ranger, and have received "in excess of 100" tips on the case.
