German-Americans are the largest self-reported ancestral group in the United States. Correspondingly, there are hundreds of large and small Oktoberfest celebrations held annually throughout the country, the largest being Oktoberfest Zinzinnati in Cincinnati, Ohio.
Known for its large German immigrant population, the Commonwealth of Pennsylvania and its historic Pennsylvania Dutch (Pennsylvania Deutsch) population are well known to have many Oktoberfest celebrations during the months of September and October. These celebrations became increasingly popular among the general Commonwealth population in the later half of the 20th century with the rise of microbreweries, and with the opening of authentic German brew houses such as Hofbrauhaus in Pittsburgh, PA.
The Oktoberfest is an important part of Bavarian culture, having been held since 1810. Other cities across the world also hold Oktoberfest celebrations, modelled after the original Munich event.
The Munich Oktoberfest originally took place during the 16 days up to, and including, the first Sunday in October. In 1994, the schedule was modified in response to German reunification so that if the first Sunday in October falls on the 1st or 2nd, then the festival would go on until October 3 (German Unity Day). Thus, the festival is now open 17 days when the first Sunday is October 2 and 18 days when it is October 1.
In 2021 Oktoberfest in USA falls on September 18.