O'BRIEN, MARY CATHERINE, age 85, passed away December 20, 2020 in Newport Beach, CA. Mary is the daughter of the late Joseph Leo and Agnes (nee Salchert) Marcero of Pontiac, Michigan. She graduated from St. Frederick's High School in Pontiac, MI and later Mercy College of Detroit. Before retiring, Mary was a dedicated teacher at the Whitmer Human Resource Center, Pontiac School District. Mary enjoyed spending summers with her family and many friends at their cottage in Tobermory, Ontario. Mary is survived by her three children: Kathleen (Dean) Rasmussen, Mary Ellen (Thomas) Williams, and Joseph (Alicia) O'Brien. Mary is also survived by her grandchildren: Erin (David) Urbina, Jeremy Mann, Ashley Lall; Andrew, Adam, Aidan, and Alex O'Brien; and Nakia and Ella Marie Williams; her great-granddaughter, Isabella Urbina; many nieces and nephews. Mary was preceded in death by her husband, Donald Carr O'Brien and her brother, Thomas Leo Marcero. Memorial contributions can be made in Mary's name to the IHM Sisters in Monroe, Michigan. A private family graveside service will be held at Mt. Hope Cemetery in Pontiac, MI. Please keep Mary and her family in your thoughts and prayers during this time.