U.S. District Court Judge Clark Waddoups, in the decision handed down Friday, said a provision in Utah law that forbids cohabitation with another person was a violation of the First Amendment.
The ruling was a victory for the polygamist Brown family that stars in the TV reality show "Sister Wives" and other Fundamentalist Mormons who believe polygamy is the path to heaven.
Anne Wilde of the polygamy advocacy group Principle Voices says polygamous families have lived under the threat of arrest for decades and no longer have to worry that "someone will knock on their door and take away their kids" because the ruling decriminalizes polygamy in Utah.
Mormon church spokesman Eric Hawkins said Saturday that its members do not practice polygamy, and polygamist organizations have no affiliation with The Church of Jesus Christ of Latter-day Saints despite the fact the term "Mormon" is "sometimes misleadingly applied to them."
The Utah Attorney General's Office has not yet said whether it'll appeal Waddoups' decision.