Frank did a number of September titled songs: The September of My Years, September in the Rain, and September Song.
September Song was written by Maxwell Anderson Kurt Weill for a 1939 historic musical with New Deal references Knickerbocker Holiday that closed only after a few months (old peg leg character New Amsterdam Governor Peter Stuyversant sings it in that play). Bing Crosby recorded the song in the forties so Frank did too, and went back to it several times in his career. This is a song that became more popular as time went on. As always with songs Frank recorded repeatedly, it is interesting to hear his interpretation of it over time.