Hyrum Smith (1800-1844) was an early member and leader of the Church of Jesus Christ of Latter-day Saints who was martyred at Carthage, Illinois.

Hyrum Smith, the second son of Joseph and Lucy Mack Smith and older brother of Joseph Smith, Jr., was born in Tunbridge, Vermont, February 9, 1800. At nineteen he moved with his family to western New York. On November 12, 1826 he married Jerusha Barden. He was baptized by his brother Joseph in Seneca Lake in June 1829 and was one of the Eight Witnesses to see the actual gold plates of the Book of Mormon. Hyrum's wife, Jerusha, died in October of 1837, shortly before Hyrum was called as Joseph Smith's second counselor in the First Presidency of the Church. Hyrum then married Mary Fielding on December 24, 1837.

During the 1830's Hyrum served several short missions for the Church, mostly in Ohio. Hoping for a respite from religious persecution, the main body of the Church moved from Ohio to Missouri in 1838. As the oppression intensified in Missouri, however, Hyrum and his brother Joseph were incarcerated in the jail at Liberty, Missouri for about six months before escaping to western Illinois in April of 1839. Hyrum later helped establish the city of Nauvoo and held several civil and military offices in Nauvoo.

In January of 1841, Hyrum was called to be Patriarch of the Church. The office, being hereditary, was passed to him upon his father's death. He was also called to serve as Associate President of the Church in 1841. In June 1844 he was again imprisoned with Joseph. This imprisonment took place at Carthage, Illinois. On June 27, 1844 Hyrum and Joseph were both killed by a mob that stormed the Carthage jail.