A Libertyville police officer on patrol spotted the fire just after 3:20 a.m. in the 100-block of Johnson Avenue, according to law enforcement officials.
Libertyville fire crews, several other fire departments and police responded to the scene to extinguish the blaze.
Once the fire was put out and first responders searched the home, a deceased individual was found, police said.
RELATED: 'He was going to set her house on fire': Deadly Gresham fire intentionally set, family claims; 10-year-old girl, mother killed
The Libertyville Police Department, Lake County Major Crime Task Force, Illinois State Fire Marshal's Office, Libertyville Fire Department and Lake County Coroner's Office are investigating the incident.
The individual's identity is being withheld, pending notification of next of kin.
Roadways in the surrounding area, including Milwaukee Avenue, were temporarily closed during the incident.