John Denver recorded his demo of ‘Babe, I Hate to Go’ in 1966, but the song got its first proper release a year later as ‘Leaving on a Jet Plane’ by Peter, Paul and Mary, appearing on their eighth album, titled Album 1700.
The trio released the song as a single two years later and wound up with their first (and only) #1 Billboard hit. For many people, this is the version of the song they know best.