The Lake County Sheriff said that around 6 p.m., police responded to an explosion at a home in Lakes of the Four Seasons.
A family had been going through a grandfather's belongings when they found a hand grenade. It is unclear whether the pin of the grenade was pulled which caused the detonation, or whether the age of the explosive and it being handled is the reason it went off, police said.
A 47-year-old man died at the scene. His children, a 14-year-old boy and 18-year-old woman, were rushed to the hospital with injuries.
The explosion occurred in a garage area, police said.
The deceased was identified as Bryan Niedert, of Lake of Four Seasons.
The cause and manner of death will be confirmed by the Lake County Coroner’s Office through an autopsy scheduled for Monday.
The Porter County Bomb Squad was called to secure the area and determine whether there were more explosive devices.
The Lake County Sheriff's Department initially told FOX 32 Chicago News that the injured teens were two males. This story has been updated to show new ages and genders.