C. Cassilly Adams (July 18, 1843 - May 8, 1921) was an American artist who is one of two artists who is credited with creating a version of the painting Custer's Last Fight along with F. Otto Becker who modified Adams' original 1884 version. The Adams version of Custer's Last Fight was restored by a restoration in 1938. He was born in Zanesville, Ohio, to lawyer William Apthorp Adams and served in the American Civil War.
He died in Trader's Point, Indiana near Indianapolis in 1921.