Sixty-three-year-old James Morrisy was on his way to a call on Monday when his squad car was struck by another vehicle.
He later died at the hospital.
Morrisy was a 30-year veteran of the force and the first officer to die in the line of duty in the department.
"He was the epitome of a police officer," said Joe Shuringa, Oak Forest Fire Department. He's been here for 34 years and loved every single minute of it. I mean his guys and his coworkers loved him just as much as he loved the job."
Morrisy was the longest-tenured patrolman in the department.
Police say the crash was an accident and no charges will be filed against the other driver.