Just how did carving of jack-o’-lanterns become associated with the holiday and why on earth did they called jack-o’-lanterns instead of john-o’-lanterns?
According to the cyberfont of wisdom Wikipedia the use refers to the Irish custom of carving turnips into lanterns as a way of remembering the souls held in purgatory. Makes sense as most sources agree that Halloween (derived from the term All Hallow’s even (short for evening)) is of Celtic origins. Of course, when those waves of Irish hit American Shores they found the pumpkin and knew right away that it was better than a turnip (or a potato)
Sources disagree on the exact date the first official pumpkin was carved but by the end of the Nineteenth Century it was firmly established in the US.
So why jack?
Apparently, there’s a legend about this crafty Irish fellow named Stingy Jack who bested the devil several times. And when he died, neither heaven nor hell would take him in. The tale is best told here: Legend of Stingy Jack
So now there are fabulous pumpkin carving events all around the country. Many bring it to an art form such as on sites like http://www.extremepumpkins.com/