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.
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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.
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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.
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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.