Lily Cahill (July 17, 1888, Lockhart, Texas – July 20, 1955, San Antonio)  was an American actress of the stage and screen. The granddaughter of Confederate Army Colonel John Jacob Myers, she began her career in 1910 at the age of 15 playing supporting roles in several silent films directed by D.W. Griffith. In 1911 she was given leading parts in A Victim of Circumstances and The Failure.
In 1912 Cahill abandoned her movie career for the stage, making her Broadway debut in the short-lived play The Road to Arcady by Edith Sessions Tupper. She remained highly active in the New York theatre scene up through 1941. Some of her notable appearances are:
- Roi Cooper Megrue's Under Cover (1914)
- Brandon Tynan's The Melody of Youth (1916)
- Henri Lavedan's The Marquis de Priola (1919)
- Matheson Lang's The Purple Mask (1920)
- Owen Davis's Opportunity (1920)
- Arthur Goodrich's So This Is London (1922)
- Jesse Lynch Williams's Lovely Lady (1925)
- Sil-Vara's Caprice (1928)
- Rachel Crothers's As Husbands Go (1931)
- Sidney Howard's Alien Corn (1933)
- S. N. Behrman's Rain From Heaven (1934)
- George S. Kaufman's First Lady (1935)
- Howard Lindsay and Russel Crouse's Life With Father (1941)
She also made appearances on the London stage and was active in regional theatre both in the Northeast United States and in her native Texas. Cahill returned periodically to films during her career, appearing in Colonel Carter of Cartersville (1915), My Sin (1931), and So This Is London (1939). She also appeared in one episode of the television series The Philco Television Playhouse in 1953. She was briefly married to Irish-born American actor Brandon Tynan.
- 1900 US Census Records
- Passenger Manifest SS Normandie November 10, 1938
- The New York Times, July 21, 1955
- The Los Angeles Times, July 21, 1955
- San Antonio Express, November 28, 1939
- San Antonio Express, July 21, 1955
- "Lilly Cahill", Variety, July 27, 1955, p. 127.