Mary Margaret (Peggy) Cass (May 21, 1924 - March 8, 1999) was an actress and comedienne.

She was best known for her performance as Agnes Gooch in Auntie Mame on both Broadway and in the film version (1958), a role for which she received an Oscar nomination for Best Supporting Actress. Her son, Rob, has gone on to become a noted economist.

She was also a regular panelist on the television game show "To Tell the Truth".

She died of heart failure in New York City in 1999.