Although "Southwinds Hotel," where Marjorie meets Noel, is supposed to be in the Catskill Mountains (NW of New York City), the movie was actually filmed at Schroon Lake, in the Adirondack Mountains (NE of New York City).
Warner Bros. tested singer/actress Erin O'Brien for the lead in Marjorie Morningstar. When she met Gene Kelly, the male lead in the movie, he said, "Miss O'Brien, I feel you're too tall for the part." So she asked to be let out. But Warner signed her anyway, for four westerns, two feature films, and seven network TV shows.
For her performance in this film, Carolyn Jones won a Golden Globe in the now-defunct category "Most Promising Newcomer - Female". Along with her Oscar nomination for The Bachelor Party (1957), it was the only major recognition Jones received from her peers during her career.