Daniel Anthony O'Connor

Daniel Anthony O’Connor III, of Groton, Massachusetts, passed away on July 2, 2025, at Massachusetts General Hospital in Boston. He was 74.

Born in Troy, New York in 1951, Daniel led an extraordinary life filled with devotion to his work, his hobbies, and above all, his family. He is survived by his beloved wife of 49 years, Helen Kane O’Connor; his children—Annie and her husband Anthony Fiandaca of Bolton, Anthony and his wife Jillian of Newton, and Nicholas and his wife Margret of Lunenburg; his grandchildren—Milo, Nico, Ella, Kieran, John, Daniel, and Mae. He also leaves behind his mother Margaret O’Connor of Troy, NY; siblings—John (Sue) of Stow, MA; Joe (Constance) of Woodbridge, Connecticut; Mike (Lori) of Manteo, NC; and Patricia of Troy, NY; as well as many nieces and nephews, brother and sisters in-law and lifelong friends.

Daniel earned a BA in electrical engineering from Clarkson University, followed by an MS and PhD in systems science and mathematics from Washington University. He spent over four decades at MIT Lincoln Laboratory, where he specialized in air, missile, and maritime defense strategy—making profound contributions to national security.

A man of many passions, Daniel was an avid sailor of his sailboat "The Folly V", a lifelong hockey player, and an enthusiastic student of history, education, and music. His adventurous spirit led him and Helen from Nantucket, MA, where they met, to Wellfleet, Cape Cod—where they married in 1976—to Potsdam, NY; St. Louis, MO; Townsend, MA; the Kwajalein Atoll in the Marshall Islands; and finally, their cherished home in Groton.

Daniel will be remembered for his kindness, his generosity, his taste for adventure, and his love of family.

The O’Connor family wishes to extend heartfelt thanks to the nurses, doctors, and support staff of Lunder 10 at Massachusetts General Hospital for their exceptional care.

A funeral mass for Daniel will be held on Thursday, July 31 at 1 PM at Saint James Parish, 13 St. James Ave., West Groton, MA. In lieu of flowers, please consider a donation to the Mass General Hospital Cancer Center or a blood donation to the American Red Cross.

Arrangements are under the care of Badger Funeral Home, A Life Celebration Home, 45 School St., Groton, MA 01450.