This is a story I read online, just thought I would share:
Why Carve Pumpkins?
The story of the Jack o'Lantern comes from Irish folklore.
Jack was a crafty farmer who tricked the Devil into climbing a tall tree. When the Devil reached the highest branch, Jack carved a large cross in the trunk, making it impossible for the Devil to climb down. In exchange for help getting out of the tree, the Devil promised never to tempt Jack with evil again. When Jack died, he was turned away from Heaven for his sins and turned away from Hell because of his trickery. Condemned to wander the earth without rest, Jack carved out one of his turnips, took an ember from the devil, and used it for a lantern to light his way. He became known as "Jack of the Lantern."