Catherine Mary Casey
- Born: 1864, Canada
- Died: 1950, Pembroke, Ontario aged 86 17
- Buried: Grey Nuns cemetery
Sister St. Mark entered as a Novitiate of the Grey Sisters of the Immaculate Concepition in 1884 and worked as a teacher in Ottawa, Hawkesbury, Midland, Timmins, and Pembroke.
Alma (Brennan) O'Hara (whose mother was Jane (Casey) Brennan, sister of Sr. St. Mark) told of how when she was a child she asked her aunt, Sr. St. Mark, how she managed in the nun's habit in hot weather. Sr. St. Mark said, "I don't know about the others but on really hot summer days I don't wear any panties. Every now and then I get a lovely cool breeze." For the rest of her life, Alma wondered about every nun she saw on a hot summer day.
Noted events in her life were: