“MacArthur Park” was written and composed by Jimmy Webb in the summer and fall of 1967 as part of an intended cantata. Webb brought the entire cantata to The Association, but the group rejected it.  The inspiration for the song was his relationship and breakup with Susie Horton.  MacArthur Park, in Los Angeles, was where the couple would occasionally meet for lunch and spent their most enjoyable times together.  At that time (the middle of 1965), Horton worked for Aetna insurance, whose offices were across the street from the park.  When asked by interviewer Terry Gross what was going through his mind when he wrote the song’s lyrics, Webb replied that it was meant to be symbolic and referred to the end of a love affair.  In an interview with Newsday in October 2014, Webb explained:

Everything in the song was visible. There’s nothing in it that’s fabricated. The old men playing checkers by the trees, the cake that was left out in the rain, all of the things that are talked about in the song are things I actually saw. And so it’s a kind of musical collage of this whole love affair that kind of went down in MacArthur Park…. Back then, I was kind of like an emotional machine, like whatever was going on inside me would bubble out of the piano and onto paper.

Webb and Horton remained friends, even after her marriage to another man. The breakup was also the primary influence for “By the Time I Get to Phoenix“, another song written and composed by Webb.

The idea to write and compose a classically structured song with several movements that could be played on the radio came from a challenge by music producer Bones Howe, who produced recordings for The Association.