Merle Louise Letowt was born on April 15, 1934, in Manhattan and grew up largely in Bethlehem, Pa. Her father, Alvin Letowt, was a machine-shop inspector at Bethlehem Steel; her mother, Merle (Barnes) Letowt, managed the home. Merle dropped her surname soon after appearing in “Gypsy.”
She acted in high school productions and, after graduation, took a job operating a mechanical calculator for the Lehigh Valley Railroad. Her earnings helped pay for acting lessons in New York on nights and weekends; she rode the railroad there free of charge.
She performed in regional productions of “The Boy Friend,” “Born Yesterday,” “Carousel” and other shows. In 1956, she nearly made her Broadway debut in a musical called “Four Dolls on a Dime,” and the railroad agreed to give her a six-month leave of absence so she could be in the show. But shortly before rehearsals were to begin, the show was canceled.
“And I had to go back to work on Monday,” she told the interviewer Rian Keating in 1984.
She met Peter Simon, an actor and lighting designer, in 1963, while they were working at the Barn Theater, in Augusta, Mich. They married later that year.
In addition to the four Sondheim shows, Ms. Simon appeared on Broadway in three other musicals: “La Cage aux Folles” (1987); “Kiss of the Spider Woman” (1993); and “Billy Elliot: The Musical” (2008). She also performed in another Sondheim show, “A Little Night Music,” at the North Shore Music Theater, in Beverly, Mass., in 2000. She played Madame Armfeldt, a former courtesan and the mother of the character Desiree, who sang “Send in the Clowns.”
