Brigham died due to a ruptured appendix

Brigham Young vigorously opposed Utah's participation in the Civil War, especially after the Morrill Anti-Bigamy Act, which effectively forbade plural marriage in U.S. territories, was passed in 1862. Congress had previously rejected requests for Utah statehood. Later, the law led to charges against a number of church leaders, including Young. Young was not found guilty, but a case involving his secretary, George Reynolds, reached the U.S. Supreme Court, which ruled in 1879 that polygamy was not protected by the First Amendment and that the law was constitutional. Although Young's health started to deteriorate by the summer of 1877, he continued to be an active member of the Mormon church right up until his passing.

Brigham Young passed away in Salt Lake City on August 29, 1877, at the age of 76. Although the precise reason of his death is unknown, it is thought that an appendix rupture was the culprit.

His final words were "Joseph! Joseph! Joseph!"—a reference to the late Joseph Smith Jr., the movement's founder. Young's funeral was held at the Tabernacle on September 2, 1877, with anywhere between 12,000 and 15,000 people in attendance. In the center of Salt Lake City, he is buried on the grounds of the Mormon Pioneer Memorial Monument. On June 10, 1938, members of the Young Men and Young Women groups, which he created, erected a bronze memorial at the grave site.