The high court affirmed a decision by an appellate court last week, saying Child Protective Services failed to show an immediate danger to the more than 400 children swept up from the Yearning For Zion Ranch nearly two months ago.
On the record before us, removal of the children was not warranted, the justices said in their ruling issued in Austin.
The high court let stand the appellate court's order that Texas District Judge Barbara Walther return the children from foster care to their parents. It's not clear how soon that may happen, but the appellate court ordered her to do it within a reasonable time period.
The ruling shatters one of the largest child-custody cases in U.S. history. State officials said the removals were necessary to end a cycle of sexual abuse at the ranch in which teenage girls were forced to marry and have sex with older men, but parents denied any abuse and said they were being persecuted for their religious beliefs.
The case before the court technically only applies to 124 children of the 38 mothers who filed a complaint that prompted the ruling, but it significantly affects nearly all the children since they were removed under identical circumstances.
The ranch is run by the Fundamentalist Church of Jesus Christ of Latter Day Saints, which teaches that polygamy brings glorification in heaven. It is a breakaway sect of the Mormon church, which renounced polygamy more than a century ago.
Texas officials claimed at one point that there were 31 teenage girls at the ranch who were pregnant or had been pregnant, but later conceded that about half of those mothers, if not more, were adults. One was 27.
Under Texas law, children can be taken from their parents if there's a danger to their physical safety, an urgent need for protection and if officials made a reasonable effort to keep the children in their homes. The high court agreed with the appellate court that the seizures fell short of that standard.