Police were called at about 5:47 p.m. after a body was found at the Lake Forest Open Lands: Derwen Mawr Nature Preserve, according to the Lake County Coroner's Office.
The man was identified as 79-year-old John Abendshien of Lake Forest.
An autopsy was scheduled for Thursday, the coroner's office said.
"This is believed to be an isolated incident with no threat to the community at this time," the coroner's office said.
Last Thursday, Abendshien was arrested charged for allegedly having child sex abuse materials, Lake Forest police said.
He was released with conditions on Friday.
Abendshien was the original owner of the Winnetka home at 671 Lincoln Avenue.
ABC7 spoke with him last year on his memoir: "Home but Alone No More."
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No other information was available.