Police declined to release the name of the man, but said he is from the Grand Haven area.
A resident in the 7100 block of Cooley Road reported she had discovered an unknown 18-year-old male sleeping inside her vehicle, which was parked inside her garage, and called police at about 11 a.m. Sunday.
Fruitport Township police officers said they found the man to be intoxicated and still sleeping inside the vehicle.
The investigation revealed that the man might have wandered away from a party that took place the prior night at another house in the area.
Police are continuing to investigate the incident.