Mark S. Thetford of Tulsa, Oklahoma, passed away on August 31, 2026, at the age of 70.

Mark was born on August 25, 1956, in Oklahoma City, Oklahoma, to Jerry Bailey Thetford and Mary Bea Thetford. He attended the University of Oklahoma, where he earned his degree in BBS. After college, Mark worked briefly as a landman before attending Oklahoma City University School of Law. He earned his Juris Doctor and was admitted to the Oklahoma Bar in 1988, beginning a legal career that would span nearly four decades.

Mark loved being a lawyer. He was an accomplished trial attorney who tried numerous jury cases in Oklahoma and in federal courts across the country. Throughout his career, he practiced in many areas of law, including civil litigation, personal injury, criminal law, and government and tribal law. He earned an AV Preeminent rating from Martindale-Hubbell, its highest peer rating for professional excellence and ethical standards. Those who worked with Mark recognized not only his knowledge and skill, but also his judgment, compassion, and dedication to the people he represented.

Later in his career, Mark served as a prosecutor for the Muscogee (Creek) Nation, practicing during a significant period of change in Oklahoma and tribal criminal law. He was serving the Nation when the United States Supreme Court issued its landmark decision in McGirt v. Oklahoma in 2020 and continued his work through the significant jurisdictional changes that followed. Before retiring, Mark served as an Assistant District Attorney for Creek County. Public service was the final chapter of a long and varied career in a profession Mark genuinely loved.

But as much as Mark valued his work, the relationships in his life meant far more to him.

Mark shared a special bond with his brother, John. Their lives remained closely connected through adulthood, from attending law school together to raising their families. Mark was also exceptionally close to his mother, Mary, whose passing in 2025 was a profound loss. Family was important to Mark, and the Thetford family shared a closeness that included Sunday dinners, family vacations, and countless memories that will be treasured for years to come.

Above all, Mark loved his daughter, Mary Grace. He was immensely proud of her and all that she accomplished. He took great joy in watching the person she became, and anyone who knew Mark knew how readily-and proudly-he spoke about his daughter. His love for Mary Grace and the pride he took in her were among the greatest joys of his life.

Mark will also be remembered for his humor and unmistakable sarcasm. He could find something to joke about in almost any situation, including himself, and he was rarely without an opinion. His sense of humor was simply part of who he was and brought a lot of laughter to the people who knew and loved him.

Beneath the humor and sarcasm was a deeply compassionate and sentimental person who cared tremendously about the people around him. Mark was grateful for the friendships he made throughout his life and was fortunate to have family, friends, and colleagues who loved him deeply and stood by him throughout the years.

Mark also had a lifelong love of dogs, especially Golden Retrievers. They brought him companionship and happiness throughout his life and always held a special place in his heart.

Mark was preceded in death by his father, Jerry Bailey Thetford; his mother, Mary Bea Thetford; and his stepfather, Gene Stipe.

He is survived by his daughter, Mary Grace Thetford Harvey, and her husband, Kody Harvey; his brother, John Thetford; his sister-in-law, Barbara Thetford; his nephews, Grant (Amber) Thetford, Paul (Erin) Thetford, and Michael Thetford; his step-mother, Linda Thetford; and the many friends, colleagues, and loved ones who cared for him deeply.

Mark leaves behind a life defined not only by the work he was proud to do, but by the people he loved, the friendships he built, the family he cherished, and the laughter he brought with him along the way. He will be deeply missed by the people who loved him and will always be remembered for his quick wit, his big heart, and the many memories he made along the way.