The accident happened on the family farm at Church Cross, Skibbereen, at about 6.30pm.
How the accident occurred was being investigated last night, but it is understood that the boy, named locally as Ciaran Casey, was crushed between the bucket of a digger and a shed. He was found by his father.
His body was removed to CUH for autopsy this morning.
Gardaí sealed off the scene for a technical examination. The Health and Safety Authority has been informed.