A federal judge with the US District Court in Utah ruled portions of the state's anti-polygamy law unconstitutional, effectively decriminalizing the practice of polygamous cohabitation. The Salt Lake Tribune explains:
[Judge Clark] Waddoups' ruling attacks the parts of Utah's law making cohabitation illegal. In the introduction, Waddoups says the phrase "or cohabits with another person" is a violation of both the First and 14th amendments. Waddoups later writes that while there is no "fundamental right" to practice polygamy, the issue really comes down to "religious cohabitation." In the 1800s — when the mainstream LDS Church still practiced polygamy — "religious cohabitation" in Utah could have actually resulted in "multiple purportedly legal marriages." Today, however, simply living together doesn't amount to being "married," Waddoups writes.
So polygamists in Utah can't apply for multiple marriage licenses, but neither can they be prohibited from living together as (generally) husband and wives.
In not ruling to overturn Utah's anti-polygamy law in whole, the judge argued that the plaintiffs hadn't proven the 1973 statute was a successor law to the patently anti-Mormon laws that preceded it. From the ruling:
As far as bigamy is concerned, therefore, it has not been sufficiently established that the Statute is necessarily a continuation of the federal government's nineteenth-century legislation at issue in Reynolds and Late Corp. It would be ludicrous to suggest that the federal legislation at issue in those cases did not specifically target the LDS Church and its practice of polygamy. If it had been sufficiently established and argued that the Statute was an extension of that legislation, the court would likely be pressed to find it is therefore not a neutral law of general applicability on that basis and would be required to apply strict scrutiny to the polygamy part of the law as well,
The case was brought to court by Kody Brown, who is married, lives with, and has children with four wives, and whose family is featured in TLC's Sister Wives. Most polygamists' lifestyles are not as public as the Browns', so the issue may not have come to a head absent the reality show. Connor Boyack of the libertarian Libertas Institute in Utah explains:
"With rare exceptions like Kody Brown and his wives, most polygamists throughout Utah have been living under a shroud of secrecy, forced into the shadows because the government has historically considered their lifestyle to be criminal activity. Today marks a new beginning, and an important invalidation of an unjust law."
"While child brides, abuse, and other problematic activities should be dealt with and appropriately prosecuted, consenting adults in a plural relationship should not be threatened with punitive action. Judge Waddoups' ruling will help integrate these communities into society so that when abuse does occur, it will be more willingly reported and investigated."
You can read the whole ruling, via the Libertas Institute, here (pdf).
Reason's Scott Shackford explained last year how the expansion of the legal definition of marriage (and, ultimately, the regulatory structure around it) will help make the libertarian case for pulling marriage and voluntary relations between two (or more!) people out of the realm of government, something this ruling is likely to contribute to as well.