Of course, people always wonder why Oktoberfest starts in September when the name clearly implies a festival dedicated to the following month. To answer that, I’ll go back to a post I originally wrote way back in 2004:
The timing of Oktoberfest is dependent upon the first Sunday in October: it always starts in mid-September, and ends 16 days later on that first Sunday…. As to why, this is from the official Oktoberfest site:
The first Oktoberfest was held in the year 1810 in honor of the Bavarian Crown Prince Ludwig’s marriage to Princess Therese von Sachsen-Hildburghausen. The festivities began on October 12, 1810 and ended on October 17th with a horse race. In the following years, the celebrations were repeated and, later, the festival was prolonged and moved forward into September.
By moving the festivities up, it allowed for better weather conditions. Because the September nights were warmer, the visitors were able to enjoy the gardens outside the tents and the stroll over "die Wiesen" or the fields much longer without feeling chilly. Historically, the last Oktoberfest weekend was in October and this tradition continues into present times.
Old habits and names die hard. Plus, "Oktoberfest" has a nicer ring to it than "Septemberfest."