Mary Madden Lilly (July 18, 1859, in Roxbury, Massachusetts[1] – October 11, 1930, in Brooklyn, New York[2]) was a Progressive Era activist who had a prominent role in New York City's social reform movements during the last decades of the 19th century and early decades of the 20th century.

In particular, Lilly supported prison reform in the form of separate facilities for females who were first time offenders.

[8] Lilly joined The Association of Retired Teachers of the City of New York and held the position of secretary.

[3] Lilly was the recording secretary and the Chair of the Probation Committee of the New York City Federation of Woman's Clubs.

Through her affiliation with the Federation, in 1913, she worked to establish the Kingsboro House, a detention home for young women first offenders in Brooklyn.

Lilly answered the charge by asserting that she was assured by her counsel that she had the right to accept a job with the City of New York while employed in a public office with the state.

By the time that Lilly retired in 1928, she had worked under three Commissioners: James A. Hamilton, Frederick A. Wallis and Richard C.