The celebration began as a Pennsylvania German custom in southeastern and central Pennsylvania in the 18th and 19th centuries. It has its origins in ancient European weather lore, wherein a badger or sacred bear is the prognosticator, as opposed to a groundhog. It also bears similarities to the Pagan festival of Imbolc (the seasonal turning point of the Celtic calendar, which is celebrated on February 2 and also involves weather prognostication, and to St. Swithun's Day on July 15.
The groundhog (Marmota monax) is a rodent of the family Sciuridae, belonging to the group of large ground squirrels.
Banner of Grundsow Lodsh Nummer Sivva (Groundhog Lodge Number Seven), of Pennsburg, Pennsylvania.
The first documented American reference to Groundhog Day can be found in a diary entry dated February 4, 1841, of Morgantown, Pennsylvania, storekeeper James Morris:
Last Tuesday, the 2nd, was Candlemas day, the day on which, according to the Germans,the Groundhog peeps out of his winter quarters and if he sees his shadow he pops back for another six weeks nap, but if the day be cloudy he remains out, as the weather is to be moderate.