Mary Day

Mary Day may refer to:

People

 * Mary Day (dance teacher) (1910–2006), founder of The Washington Ballet
 * Mary Anna Day (1852–1924), American botanist and librarian
 * Mary E. Day, in the 2005 Supreme Court opinion Varian v. Delfino
 * Mary L. Day (1836–?), American memoirist
 * Mary Gage Day (1857–1935), American physician and medical writer
 * Mary Louise Day (1968–2017), teenage girl who mysteriously disappeared from her home

Days

 * Marian feast days