What date is referenced in the 1971 song "September" by Earth, Wind & Fire?

The 1971 song "September" by Earth, Wind & Fire references the 21st of September. This date is significant because it marks the beginning of autumn in the Northern Hemisphere, as well as being a representation of happy memories and the joyous feelings associated with the arrival of the season. The lyrics of the song convey a sense of celebration, love, and dancing, making the 21st of September an ideal date to capture the joyful essence and the positive energy that the band wanted to evoke.