(Adds reaction from TV star and others)
By Jennifer Dobner
SALT LAKE CITY, Dec 13 (Reuters) - A U.S. federal judge struck down a portion of Utah's bigamy laws as unconstitutional on Friday, siding with a reality television star and his four wives.
Polygamy is illegal in all 50 states. But Utah's law is unique in that a person can be found guilty not just for having two legal marriage licenses, but also for cohabiting with another adult in a marriage-like relationship when they are already legally married to someone else.
U.S. District Judge Clark Waddoups ruled that the second aspect is too broad because it bars consenting adults from living together and criminalizes their intimate sexual relationships.
He said the law violates both the First Amendment's clause ensuring religious rights and the Fourteenth Amendment's due process clause designed to ensure liberty.
The rest of Utah's bigamy law remains intact under the ruling, so only individuals who fraudulently obtain multiple marriage licenses would be guilty.
Utah is the headquarters state of the Church of Jesus Christ of Latter-day Saints, or Mormons, which abandoned polygamy in 1890 as Utah was seeking statehood. Some sects and breakaway groups, however, follow the early theological doctrine of plural marriage, thought to bring exaltation in heaven.
State attorneys have used the cohabitation portion of Utah's law to prosecute Utah polygamists for bigamy. It is punishable by up to five years in prison.
The ruling was a victory for Kody Brown and the four women he publicly lives with on the TLC television show "Sister Wives."
The family and their 17 children who formerly lived in Lehi, Utah, are members of the Apostolic United Brethren, a Utah-based church that follows plural marriage doctrine.
They fled to Nevada to avoid a bigamy prosecution after authorities launched a probe into their lifestyle.
No charges were ever brought, but Brown and his wives - Meri, Janelle, Christine and Robyn - launched a federal lawsuit in 2011 contending that Utah's ban on multiple marriage partners violated their right to privacy and criminalized their sexual relationships.
Kody Brown praised Waddoups "courageous decision" in a statement on Friday evening.
"We hope that in time all of our neighbors and fellow citizens will come to respect our own choices as part of this wonderful country of different faiths and beliefs," Brown said.
Waddoups ruling amounted to a "victory not for polygamy but privacy in America," said family attorney Jonathan Turley.
In his ruling, Waddoups also said Utah had incorrectly equated private sexual relations between unmarried persons with marriage and used that as a basis for prosecution, many of which he called "random at best."
Virtually all of those charged had been engaged in religiously-motivated relationships, the judge said.
The Utah Attorney General's Office said it had not seen the ruling on Friday evening, adding that it would determine whether to appeal the decision. (Editing by Eric M. Johnson and Lisa Shumaker/Jeremy Gaunt)