FAA spokeswoman Elizabeth Isham said the plane was operating by so-called "visual flight rules," meaning the pilot looked out the window to see where he was headed. The plane was not in touch with air traffic control. Conditions in the area have been overcast and rainy.
A prominent businessman from a town near Indianapolis was dropping off his daughter at Wheaton College when their plane crashed.
The former president of the pilot club that owns the plane confirmed that the crash killed Marion businessman Ray Harris.
Along with the student, another daughter and an unidentified male were killed.
Witnesses say the one-engine Cirrus SR-20 aircraft went down just before 10:30am Saturday in farmland near Ridgefiled Road and Route 14.
Emergency personnel rushed to the scene after dozens of calls from passersby and motorists to 9-1-1 for help.
Darren Smith said he rushed to the crash scene from his nearby tree farm when he heard what sounded like an airplane in trouble.
"I saw it a split second before it hit the ground," Smith told the (Arlington Heights) Daily Herald. "It was a horrific crash, pretty much nose first into the ground. The impact was tremendous.
"We tried to help, but there was no help that could be given," he said.
A parachute that's designed to help this plane if the pilot gets in trouble was hanging from a tree as federal investigators decended on the crash scene.
The aircraft was registered to the Marion Flying Cub in Marion, Ind.
The organization's president would only confirm that the craft left Marion at 9:30 a.m. and was headed to a destination north of Chicago.
It's still unclear if the aircraft had a Black Box recorder. Authorities said the craft was traveling north before the crash and that although the pilot had radio contact with a control tower, there was no mayday call made.
"On this particular craft, I am not sure what the level of that recording was," said Tim Sorensen of the National Transportation Safety Board. "It may have had some. That is one of the things we will be looking for."
The Associated Press contributed to this report.