The first patent for something resembling a disco ball was issued in 1917. However, disco balls have been used since 1897 up until this point. They become very popular in the 1920s and lasted well into the Disco Era.
Sources:
https://en.wikipedia.org/wiki/Disco_ball
https://www.thevintagenews.com/2017/03/05/disco-balls-existed-long-before-their-heyday-in-the-1970s/