Police responded at about 8:50 p.m. to the 24100-block of West Main Street.
A 16-year-old was shot in a car and initially drove himself to the Plainfield Fire Department and he was then transported to the hospital, police said. The victim's condition was not immediately known.
There was an hours long investigation at an apartment building near Route 59 and Main Street.
It is not known what led up to the shooting, but police said the victim knows the 18-year-old suspected shooter, who is not in custody.
Police said it is an isolated incident and there is not a threat to the public.