The celebration, which began as a Pennsylvania German custom in southeastern and central Pennsylvania in the 18th and 19th centuries, 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 1 and also involves weather prognostication and to St. Swithun's Day in July.
Meteorological Accuracy.

The largest Groundhog Day celebration is held in Punxsutawney, Pennsylvania, where crowds as large as 40,000 have gathered to celebrate the holiday since at least 1886. Other celebrations of note in Pennsylvania take place in Quarryville in Lancaster County, the Anthracite Region of Schuylkill County, the Sinnamahoning Valley and Bucks County.

Outside of Pennsylvania, notable celebrations occur in the Frederick and Hagerstown areas of Maryland, Marion, Ohio with Buckeye Chuck, the Shenandoah Valley of Virginia, Woodstock, Illinois, Lilburn, Georgia, among the Amish populations of over twenty states and at Wharton, Ontario, and Shubenacadie, Nova Scotia, in Canada. The University of Dallas in Irving, Texas, has taken Groundhog Day as its official university holiday and organizes a large-scale celebration every year in honor of the Groundhog.

According to Groundhog Day organizers, the rodents' forecasts are accurate 75% to 90% of the time. However, a Canadian study for 13 cities in the past 30 to 40 years found that the weather patterns predicted on Groundhog Day were only 37% accurate over that time period--a value not significant compared to the 33% that could occur by chance. According to the StormFax Weather Almanac and records kept since 1887, Punxsutawney Phil's weather predictions have been correct 39% of the time. The National Climatic Data Center reportedly has stated that the overall accuracy rate is around 61%.