At the time of the 1880 Federal Census, John Casey, a coal miner born in Scotland, and his wife, Annie, born in Maryland, were residents of Barton, Allegany County, Maryland. Their only child was Ellen, born in Maryland the previous November.

In 1900, "Ella" Casey, 20, and John Casey (Jr.), 19, both born in Maryland, were living in Pittburgh with their aunt and uncle, William and Mary Condon.

In 1910, Ellen T. Casey, 27, a dressmaker, and her grandmother, Ellen M., 69, were living with the Condon family. Ellen M., born in Scotland, is listed as the mother of Mary T. Condon, so Ellen T. was the daughter of Mary T.'s brother. It is not known what happened to Ellen's parents, John and Annie.

Ellen Theresa Casey is named in a 1922 history of the Pittsburgh Red Cross as a St. Francis nurse graduate who was "in active service with the American Expeditionary Forces and in the United States." The Department of Veterans Affairs Death File indicates that Ellen Casey was born on November 14, 1879, and she died on September 4, 1978. She served in the U. S. Army Nurse Corps, from April 3, 1918 through June 3, 1918.