Dr. John Frank O'Brien

Dr. John Frank O'Brien, 84, of Oronoco, Minnesota passed away on Sunday, October 4, 2026 at Rochester Rehabilitation and Living Center in Rochester, Minnesota surrounded by family. He was born on May 20, 1942 in Winona, Minnesota to Harold John and Jeanette Eleanor (Salisbury) O'Brien. The family moved many times during John's childhood due to his father's employment.

John graduated from John Marshall High School in Rochester, class of 1960. He went on to receive his bachelor's in chemistry from Winona State University in 1964 and then his PhD in biochemistry from Kansas State University on a NASA scholarship in 1968. John also did some post-graduate work at the University of Wisconsin - Madison and during that time two years of his study was in Kiel, Germany. He then moved back to Madison, Wisconsin to work for the University of Wisconsin for 9 years. During that time, he developed mass spectrometry assays and wrote many published journal articles on genetic diseases, including metabolic childhood diseases. In 1979, John began employment in the Biochemical Genetic Laboratory at Mayo Clinic, Rochester, until his retirement in May of 2008 after 30 years of service.

John was united in marriage to Terri Cutting in 1964 and to this union had two children, Krista and Patrick. They later divorced in 1988. John was later united in marriage to Amy Groszbach in 2012. John enjoyed spending time with family and attending family events. He also loved driving the Polaris Ranger, fishing for walleye, deer hunting in northern Minnesota, and gardening on a small farm. He especially enjoyed using his two-row corn planter for his sweet corn plot.

John is survived by his wife of 14 years, Amy; children, Krista O'Brien and Patrick O'Brien; and several nieces and nephews. He was preceded in death by his parents, Harold and Jeanette; siblings, Richard "Dick" O'Brien, Jane Streiff and an infant twin sister to Jane, and Daniel O'Brien. A private family service will take place at Zumbrota Cemetery in Zumbrota, Minnesota. Memorials can be directed to the Oronoco Fire Department and First Responder organization. Arrangements were entrusted to the Mahn Family Funeral Home, Larson Chapel in Zumbrota.