Frances Lillian Ilg (1902– July 26, 1981) was an American pediatrician and professor at Yale University.

In 1950, she co-founded the Gesell Institute in New Haven with two colleagues, psychologist Louise Bates Ames and Janet Learned Rodell.

[5] In the 1950s and 1960s she counseled parents to "enjoy their children" and "guard their sense of fun and sense of humor"; she also advised school districts to consider emotional maturity as well as intellectual development in grade placements.

[7] In 1957 she received the William Freeman Snow Award from the American Social Hygiene Association, for "distinguished service to humanity.

[9] Ilg died in 1981, aged 78 years, while vacationing in Manitowish Waters, Wisconsin.