In the 1870s the Church of Jesus Christ of Latter-day Saints (AKA the Mormon Church) found itself facing the Morrill Anti-Bigamy Act. The Act, known to be a direct response to their practice of polygamy, explicitly banned the practice of marrying multiple people (AKA bigamy) in the United States territories, which at the time included Utah where the Mormon Church had settled.
In response, the Mormon Church decided to do a “test case.” They asked George Reynolds, then a secretary in the office of the President of the Church if he’d be the defendant. When he agreed, they gave US Attorney William Carey witnesses who could testify that Reynolds had two wives. Carey charged Reynolds under the Act, and Reynolds was indicated for bigamy by a Grant Jury on Halloween, 1874, with a punishment of two year hard prison labor and a $500 fine.
Reynolds appealed, saying his conviction should be overturned because 1) it was his religious duty to marry multiple times and the First Amendment protected this; 2) his grand jury had not been legally constituted; 3) that challenges of certain jurors were improperly overruled; and 4) that testimony was not admissible as it was under another indictment.
The Supreme Court held unanimously against Reynolds. Chief Justice Waite, who wrote the opinion, noted a ban on bigamy had existed in English Law for over 200 years. Waite also pointed out the First Amendment made distinctions between religious belief and action (or, as we’d say today, practice), and that it didn’t prevent legislation from restricting practice since otherwise everyone would put their religion over the law…which defeats the point of having laws in the first place.
Waite and the other justices also went on to rule against Reynold’s other grounds saying (broadly) the jury had been constituted correctly and Reynolds hadn’t made the most of his opportunities in court. There was, one (minor) dissent : Justice Field argued one piece of testimony shouldn’t have been admitted, but this is mostly overlooked since he concurred everywhere else.
The immediate reaction was what you’d expect. George Cannon (who represented Utah and was a Mormon) condemned the decision, saying it encourages prostitution, bastardy, and infanticide. The New York Times praised the decision, saying it extended the Common Law that existed everywhere else to Utah.
Today these laws still stand, though, ah, there are people that are in polyamorous relationships. But it’s not something the Mormon Church worries about anymore: it too rejected polygamy starting in 1890 as part of trying to ensure Utah’s statehood.