John Devn Cornish was born in Salt Lake City, Utah, on April 12, 1951. He married Elaine Simmons in August 1973. They are the parents of six children. Elaine Cornish passed away from cancer in June of 2019. Elder Cornish married Rosanne Brown in May of 2021.
He received a bachelor of arts degree in biology from Johns Hopkins University in 1975. In 1978 he received a doctor of medicine, also from Johns Hopkins University.
He has served in numerous Church callings, including full-time missionary in the Guatemala–El Salvador Mission, bishop, stake president, and president of the Dominican Republic Santiago Mission (2003–2006). At the time of his call, he had been serving as a member of the Sixth Quorum of the Seventy in the North America Southeast Area.
Elder Cornish is currently serving in a number of committee assignments at Church headquarters.
He completed his pediatric residency at the Boston Children’s Hospital at Harvard University in 1981. In 1985 he completed a newborn intensive care fellowship program at Wilford Hall USAF Medical Center. Subsequently, he was professor, chairman, and later a vice chairman in the Department of Pediatrics at Emory University School of Medicine.