Holden's police chief, Chris Greeley, said police responded to the parking lot near the Holden Congregational Church around 3:30 on Friday afternoon.
A passerby had seen a car parked against the woodline and realized the person in the back was deceased.
Police told us they're still working to positively identify the man, but believe him to be in his 30's and from the area.
Due to the nature of the scene, officials say they're still working to determine how the person died and are not sure if it's suspicious.
"Some time had gone by and unfortunately due to the weather conditions inside a car, the windows up and this warmth can impact the decomposition of a body," Greeley said.
The medical examiner's office is working to determine a cause of death.
Holden Police say they were assisted by the Maine State Police Major Crimes Unit.