The name Milly has its origins in the medieval English pet name or diminutive form of the female given names Millicent and Amelia. It emerged in England during the Middle Ages, likely around the 12th century.

Milly is derived from the Old German name Amalrich, which consists of the elements "amal" meaning "work" and "ric" meaning "power" or "ruler". Over time, Amalrich evolved into the Old French name Amelie and the Latin name Amelia, which later gave rise to the diminutive Milly.

One of the earliest recorded instances of the name Milly can be found in the Domesday Book of 1086, which was a comprehensive survey of landholdings and inhabitants in England commissioned by William the Conqueror. The name appears as a variation of Millicent, which was a common English name during the Middle Ages.

Throughout history, several notable individuals have borne the name Milly. One of the earliest was Milly Candler (1878-1953), an American philanthropist and the wife of Coca-Cola founder Asa Griggs Candler. Another prominent figure was Milly Barranger (1917-2008), an American theatre producer and director who was instrumental in the development of off-off-Broadway theatre in New York City.

In the field of literature, Milly Theale was a character in the novel "The Wings of the Dove" by Henry James, published in 1902. This fictional character, a young American heiress, played a central role in the novel's exploration of themes such as morality, love, and the complexities of human relationships.

In the world of sports, Milly Silcock (1908-1990) was a notable English cricketer who played for the England women's cricket team in the 1930s and 1940s. She was one of the first professional female cricketers and played a significant role in the development of women's cricket.

Another noteworthy individual with the name Milly was Milly Dowler (1988-2002), a British teenager whose tragic murder in 2002 sparked widespread public outrage and led to significant changes in the UK's legal system and media practices.