What was Peter, Paul, and Mary's only No. 1 single song as well as their final pop Top 40 Chart hit?

In 1969 "Leaving on a Jet Plane", became Peter, Paul, and Mary's only No. 1 single, as well as their final pop Top 40 Chart hit. The song had been written by John Denver, a good friend to each member making up the popular trio. The song became the group's sixth million-selling gold single.

The song track itself first appeared on their 1967 million-selling platinum certified "Album 1700" (which also contained their No. 9 hit "I Dig Rock and Roll Music"). Besides being the trio's biggest hit and becoming their only No. 1 on the Billboard Hot 100 chart in the US, the song also topped the charts in Canada, and reached No. 2 in both the UK Singles Chart and Irish Singles Chart in February 1970.

Additionally, the song "Leaving on a Jet Plane" found usage in other media. It was used on various TV shows and in movies, such as "The Rock" (1996), "Girls' Night" (1998), "Armageddon" (1998), "Superstar" (1999), "Catch Me If You Can" (2002), and in the end credits of the 2011 Irish film "The Guard".