John Murdock Jr. (July 15, 1792 – December 23, 1871) was an early convert to the Latter Day Saint movement and was a missionary for the Church of Jesus Christ of Latter-day Saints (LDS Church). Mentioned twice in the Doctrine and Covenants, he devoted most of his life to full-time missionary service for the LDS Church. He was the first mission president for the LDS Church in Australia where he oversaw the official organization of the church in the country and its early growth. A compatriot of Joseph Smith, Murdock attended School of the Prophets and participated in Zion's Camp. After the death of his first wife in childbirth, Joseph and Emma Smith adopted his infant twins. Julia Murdock Smith, who survived to adulthood, was the eldest child and only daughter of the Smiths.