Why can a Mormon in Utah practice polygamy while its virtually impossible for a Muslim to do the same?

The short answer is that neither party can practice polygamy. Polygamy is illegal in Utah; it was illegal in the Utah Territory starting in 1862 and was banned in the state’s constitution when Utah became a state in 1896. The law applies regardless of whether the parties involved are Latter-Day Saints or Muslim. The criminal penalties for polygamy were substantially reduced in February of 2020 in an effort to encourage polygamous families to report domestic abuse or other crimes, but it remains a violation of the law. Polygamy is also forbidden by the known Church of Jesus Christ of Latter-Day Saints (the group most people are referring to when they talk about Mormons, though some Latter-Day Saints regard the word “Mormon” as a pejorative).

The confusion over this may be due to the fact there are still small polygamous communities in Utah and the rest of the western United States, who have continued the practice in violation of the law. These schismatic religious groups are referred to as fundamentalist Latter-Day Saints, who separated from the better-known Church of Jesus Christ of Latter-Day Saints over their choice to continue to practice polygamy after the Church of Jesus Christ of Latter-Day Saints banned it at the end of the nineteenth century. Fundamentalist Latter-Day Saints are small demographically, having only perhaps 10,000 or so adherents among several different groups, compared to the Church of Jesus Christ of Latter-Day Saints, which currently has 16.5 million members. Fundamentalist Latter-Day Saints have sometimes been criminally prosecuted for engaging in polygamy, but often states like Utah, Arizona, and Nevada have opted to leave them alone, in part because it’s comparatively hard to find witnesses willing to testify in criminal cases in reclusive religious communities.

The practice of polygamy first appeared among Latter-Day Saints in 1830s, when the group’s founder and prophet, Joseph Smith, began to secretly take additional wives. Smith began to teach a doctrine that was sometimes called “patriarchal marriage,” “celestial marriage” or “the Principle.” Smith said that the command to do this came directly from God, but he justified it in a number of different ways. One consistent claim was polygamy should be practiced as it had been by the Biblical patriarchs. Smith also explained that polygamous marriages would enable families to remain together in heaven, a concept that was novel in Christian theology. Smith also may have connected polygamy to his teaching that human beings should “become like Gods;” marriage to multiple women in some sense aided this.

Smith was murdered in 1844, before ever publicizing this new revelation. His first wife, Emma Smith, would vigorously maintain that Smith had not been a polygamist and she and Smith’s son created a new group, the Reorganized Church of Jesus Christ of Latter-Day Saints (now called Community of Christ) that rejected polygamy. The main Church of Jesus Christ of Latter-Day Saints continued to practice polygamy in secret, and in 1852 the President and Prophet of the Church, Brigham Young, publicly announced that the church was engaged in the practice. By the late nineteenth century, perhaps 20 to 30 percent of Latter-Day Saint families were polygamous.

The United States government tried to stamp out polygamy. In 1862, the Morrill Anti-Bigamy Act, which banned men from having more than one wife and prevented any church from having over $50,000 in property, was signed by Abraham Lincoln. It was expressly designed to stamp out polygamy in the Utah Territory and destroy the influence of the Church of Jesus Christ of Latter-Day Saints.

The federal government waged a protracted battle using federal agents against polygamy in the territory. In 1878, the Latter-Day Saints lost a Supreme Court case where they had argued that banning polygamy was a violation of their religious freedom. By the 1880s, federal agents were doing regular house raids, issuing fines and imprisoning men and women regularly.

Things reached an apogee with the Edmunds-Tucker Act of 1887, which massively increased federal power to fight against polygamy. It replaced local judges with federal appointees (who would be hostile to polygamy), disenfranchised women (who were typically supportive of polygamy), disincorporated the Church of Jesus Christ of Latter-Day Saints, and seized its assets. In 1890, the Church of Jesus Christ of Latter-Day Saints gave in to the pressure, and its president Wilford Woodruff issued what came to be called the 1890 Manifesto, which banned Latter-Day Saints from practicing polygamy.

Many Latter-Day Saints continued to try to practice polygamy secretly for years after the Manifesto. However, non-Mormons were aware of this and exerted political pressure to prevent Utah from becoming a state over the issue. When Utah did become a state in 1896, it included a clause in its constitution barring polygamy, to my knowledge the only state to have such a clause. Latter-Day Saint leaders spent the next few decades trying to stop polygamy within their church, in an effort to win public approval and acceptance.

Some of the Latter-Day Saints refused to accept the Manifesto barring polygamy, and founded their own religious communities. These include the Fundamentalist Church of Latter-Day Saints, Apostolic United Brethren, and the Latter Day Church of Christ. The main Church of Jesus Christ of Latter-Day Saints regards them as apostates. Many of them have developed their own traditions over time, and now differ substantially from the Church of Jesus Christ of Latter-Day Saints in terms of theology.

I am not aware of any U.S. state or territory in which polygamy is legal. It would likely be violation of the establishment clause of the First Amendment to treat one religious group’s polygamy as different from another.