Asked about the song's meaning by Billboard magazine, Cooper replied:
"September Song" in a nutshell is a nostalgic, innocent look at a teenage romance - probably one of your first romances. Looking back as an adult now at how simple things were back then, having those moments of, like, "I wonder what that person is doing now.
In the UK, September is when you go back to school after the holiday. So that's the idea, this person has been missing this girl all summer - she's a September song, that's what he's looking forward to. We just wanted to write a song that was really sweet and innocent, it wasn't over sexualized or anything like that."