William J. Cassidy, of Billerica, passed away peacefully in his home Monday, October 15, 2012 after a brief illness. He was the beloved husband of Sarah J. (Elliott) Cassidy, to whom he was married 64 years. Born in Donegal, Ireland, on November 6, 1924, he moved to the United States in 1947. Mr. Cassidy had lived in Billerica for the past 61 years. Retired now for several years, he had been employed as a heavy equipment operator for R.H. White Construction for many years. He was a longtime active member of the Aldersgate Methodist Church in Chelmsford. Besides his wife he is survived by his two sons, William of Salem, NH, and Robert of Phoenix, AZ; his two daughters, Deborah of Tewksbury and Dorothy Newcomb of Billerica; his brothers, Robert of Woburn and Andrew of Ireland; and his sister, Elsie of Ireland. He also leaves his three grandchildren, Robert Cassidy, Erin Newcomb, and Wesley Newcomb, and his two great-grandchildren.