Sister Margaret Mary McMahon, C.S.J., a Sister of St. Joseph, Brentwood, L.I., for 76 years, died Nov. 16 in hospice care at the Sacred Heart Convent in Hempstead, L.I.

She entered the congregation in 1942 from Good Shepherd parish, Marine Park. She earned a bachelor’s degree in math from Manhattan College and a master’s degree in education/ reading from the University of Chicago, Ill.

Formerly known as Sister Denis Marie, she taught elementary grades at St. Patrick, Long Island City, 1943-44; St. Agnes Seminary, Marine Park, 1944-46; St. Christopher, Baldwin, L.I., 1946-53; Epiphany, Williamsburg, 1953-56; Holy Child Jesus, Richmond Hill, 1956-61; Sacred Heart, North Merrick, L.I., 1961-68; Sacred Heart Seminary, Hempstead, 1968-69; and the Academy of St. Joseph, Brentwood, 1967-79.

She began her longtime ministry as a reading teacher at St. Robert Bellarmine, Bayside, in 1979.

In addition to her teaching, she volunteered on the parish level and at Maria Regina Residence.

Burial was in Calvary Cemetery, Brentwood.