Police say the boy wore a full uniform, walked into the police station and even managed to get an assignment on Saturday.
They say he patrolled in a squad car for five hours, before officers noticed his uniform was a little different. The boy didn't have a gun and never drove the car. A Chicago police superintendent says they are investigating how the deception went undetected for so long.
"He is familiar with the police department environment and clearly has a keen desire to be a police officer," said Asst. Supt. James Jackson, Chicago police department.
A police spokeswoman says the boy once took part in a Chicago program for youth interested in policing.