Lake Zurich fire officials and the Lake County Coroner's Office said the body was found Sunday in debris, after the fire Saturday afternoon on Rosewood Drive in Hawthorn Woods.
Lake Zurich fire officials previously said there was a "missing husband" involved in the fire.
The deceased is believed to be a family member who did not live at the home, the coroner's office said.
The person will be identified through further scientific examination, the office said.
The lack of fire hydrants in the area caused some problems for firefighters over the weekend.
Flames were already shooting through the roof of the house when firefighters arrived. The home near Rosewood Drive and Orchard Lane was completely engulfed in flames.
"Because of the complexity, size of the fire and lack of water, the fire went to a third alarm to send resources here," Lake Zurich Fire Chief David Pilgard said.
They attacked it from several angles, containing the fire to the home where it started, but it took several hours before firefighters were able completely extinguish the flames.
Fire investigators say the family had an electronic vehicle and charging station in the garage. While they are unsure if that is where the fire started, they said it created extra challenges in putting the fire out.
The Hawthorn Woods Police Department, Lake Zurich Fire Department, local fire investigators, and the Office of the Illinois State Fire Marshal are investigating what caused the blaze.