Dr. Mark Joseph O'Neill

1939 - 2025

Dr. Mark Joseph O'Neill passed away Nov. 4th 2025, in Sun Lakes, Ariz., with his loving wife of 63 years by his side. Born in Butte, Mont. on Oct. 9th, 1939 to Dan and Mary O'Neill. He graduated from Boys Central High School in 1957. He joined the U.S. Marine force in June of 1957 and was off to California for boot camp. Mark & Diane were married June 9th, 1962 in Sheboygan, Wisc. He graduated from Marquette Dental School in 1965 in Milwaukee, Wisc. Later that year he moved to British Columbia, Canada with his wife and two children to practice dentistry. Mark loved his dental profession and was very active in his community for 27 years. He later moved to Vancouver Island to join a Dental practice and continue his passion for sailing. In August of 1994, Mark & Diane left the island to sail around the world. They sold their boat in Turkey 9 1/2 years later in 2003. They moved back to the island while spending winters in Mexico and later in Sun Lakes, Ariz.

Mark is survived by his wife, Diane; son, Mark O'Neill Jr. (Mary Jo); grandkids, Ashley O'Neill, Nick O'Neill of Milton-Freewater, Ore.; daughter, Kelly Swank (Greg); and grandson, Matthew Swank of Kelowna, B.C.; brother, Brian O'Neill (Carole) Bluffton, S.C.; Rev. Kevin O'Neill of Helena Mt.; sister, Mary Ann Hanley of Butte Mont.; sister-in-law, Ann Stevens of Siren, Wisc.; and many nephews and nieces who he loved and watched grow up.

Mark is predeceased in passing by his parents, Daniel & Mary O'Neill, Dan & Helen O'Neill, Dr. Daniel O'Neill; sister-in-law, Ellen Marie O'Neill; brother-in-law, Al Stevens. A celebration of life will be held this summer in Oregon.