Investigators believe the juvenile was on his way to carry out a school shooting at Grand Prairie Elementary School when his relative discovered that he had a gun.
The relative called 911 while pinning the juvenile down, the sheriff's office said. Deputies responded to the scene in the 2400-block of Helmar Lane in Plainfield Township just before 1 p.m. Friday.
There, deputies detained the juvenile and recovered a Glock handgun and a backpack containing multiple loaded magazines, knives, an accelerant, gloves, and other items.
The sheriff's office informed the Plainfield Police Department and Plainfield School District 202 about the incident.
There was an increased police presence at the school for the remainder of the day, which was the last day of school.
The juvenile is at a hospital after making suicidal and homicidal statements to first responders on the scene, the sheriff's office said.
Police said there is no threat to the community, adding that this is an ongoing investigation, and no charges have been filed.
If you are experiencing suicidal, substance use or other mental health crises please call or text the new three digit code at 988. You will reach a trained crisis counselor for free, 24 hours a day, seven days a week. You can also go to 988lifeline.org or dial the current toll free number 800-273-8255 [TALK].