Maine State Police said a mechanic at Varney Chevrolet in Pittsfield found the body while working on the car.
Maine State Police Public Information Officer Stephen McCausland said the car had been towed to the dealership after it was discovered locked in a Walmart parking lot, WABI reported. It was towed to the dealership so police could get a key.
An autopsy will be performed on the body to determine the cause of death, WTMW reported.
Police would not categorize the nature of the woman's death.
A receptionist at the dealership declined to comment when reached by telephone, the Bangor Daily News reported.