Just when we had written off Peggy as the eternal perky, pug-nosed prom-queen she projected from the 1920s into the fifties, along came Mad Men, with intriguing mid-century characters with names like Joan and Betty--and Peggy, causing a bit of a re-think. MM's proto-feminist Peggy Olson was followed by Amy Adams's strong Oscar-nominated Peggy Dodd character in The Master.
Peggy has been used independently since the eighteenth century, later combined with other names such as Peggy Sue, made famous by the Buddy Holly song and the film Peggy Sue Got Married.
Some notable namesakes who have gone by Peggy include jazz singer Peggy Lee (born Norma), art patron Guggenheim (born Marguerite), skater Fleming, and author/speechwriter Noonan (born Margaret).
It's not likely that Peggy will ever regain the 31st position it held in 1937, but we can see it coming into somewhat wider use.