Mary Ann Shannon was born in February 1899 in Illinois, according to the 1900 Federal Census of Chicago. Subsequent census records give her birth place as Massachusetts. She was the daughter of Thomas Shannon, born in Illinois, and Louisa Kleasner, born in Massachusetts. In 1900, Thomas was a Switchman on the Railroad. Mary's only sibling that year was Anne, born in April 1897.

In the 1910 census, the family is found in Hopewell, Beaver County, Pennsylvania. Annie E. was 13, Mary Ann was 11, and they had two more sisters, Josephine F. and Katherine A., as well as two brothers, Thomas T. amd Patrick F. The father was a foreman of a labor gang.

Mary Shannon, 21, born in Massachusetts, was a student nurse at St. Francis at the time of the 1920 census.

About 1926, Mary married Louis Bernard Keller, born in Detroit in 1901. By the 1930 census, they had a daughter, Mary A., Jr. Louis was a manager at the AAA Auto Club, and Mary was a nurse.

Louis B. and Mary Ann Keller are listed in the 1935 census of Pinellas County, Florida with their children Mary Ann, Patricia, Jacqueline and Thomas.

Born February 22, 1899, Mary Ann Shannon Keller died in January 1976 in Coldwater, Michigan.

Mary Ann's sister, Anne, graduated from the school of nursing at St. Francis in the Class of 1917.