The state's targets are Paul Elden Kingston, John Daniel Kingston, David Ortell Kingston and 27 others - among them, children and some women.
The individuals are listed on sealed search warrants, which identify the evidence sought but not the focus of the state's investigation.
Paul Murphy, spokesman for the Utah Attorney General's Office, said the office had no comment on its ongoing investigation.
However, a state investigator confirmed the nature of the probe to Bill Morrison, Paul Kingston's attorney.
During a brief hearing in chambers Monday, 3rd District Judge Glenn K. Iwasaki denied Paul Kingston's request for a temporary restraining order to block delivery of the warrants. Morrison later said he will seek to quash the warrants, attacking them as unconstitutional.
"Once again, we have an unwanted intrusion of the Attorney General into the private lives of people who just want to live their religion," Morrison said.
Paul Kingston is the leader of the Latter Day Church of Christ, a fundamentalist Mormon sect based in the Salt Lake Valley with about 1,500 members. It is not associated with the mainstream The Church of Jesus Christ of Latter-day Saints, which prohibits polygamy.
In Utah, it is a third-degree felony to have sexual intercourse with someone who is an ancestor, descendant, brother, sister, uncle, aunt, nephew or niece. Marriages between first cousins are prohibited unless the couple is 55 and sterile or over the age of 65.
The law applies to half blood, adoptive and, when a marriage is intact, stepparent/child relationships.
Jim Hill, a state investigator, notified Paul Kingston on Oct. 17 that he was the target of a criminal investigation, according to a court document.
Paul Kingston, 46, declined to comment, but other family members defended kinship marriages as necessary given the community's small size and a desire for shared faith.
"We are a small group of people," said family member Rachel Young in a written statement. "We encourage our young people to choose companions within their own faith. This makes some related marriages inevitable. To deny the right to marry within our faith would in effect deny us the right to exist."
She also said those involved were "consenting adults;" the women named in the warrents range in age from 25 to over 40.
First-cousin marriages are permitted in at least 25 states and in many foreign countries. Half-sibling marriages are not allowed in any states.
Young accused Utah authorities of targeting her community because of its religious beliefs, adding that millions of people practice kinship marriages.
"Why is everyone tolerant of them and not us?" said Young, who was married to her first cousin, Elden Kingston. "The mass collection of DNA continues the state's effort to catalog, track and mark members of the fundamentalist community."
Former sect members say the incestuous marriages have caused genetic defects within the group, such as dwarfism, microcephaly and kidney problems.
"When you marry as close as they have through several generations, there are going to be problems," said Rowenna Erickson, who left the Kingstons years ago.
Young refuted that, saying all of the children named in the warrants are "healthy and happy, with no birth defects."
Geneticists caution that without DNA testing, it is impossible to know the cause of such defects; some research has shown only a slightly elevated risk of genetic abnormalities in first-cousin marriages.
In addition to first-cousin marriages, the Kingstons have engaged marriages between half siblings as well as uncles and nieces.
David Ortell Kingston, 40, was convicted in 1999 of having sex with his niece, Mary Ann Kingston Nichols, after she became his 15th wife at age 16.
According to a 1999 Salt Lake Tribune report and court testimony, John Daniel Kingston, 51, has children with three half-sisters.
The Tribune investigation also found Paul Kingston's plural wives included two of his half-sisters.
Jason Kingston, 31, another brother, was married to Andrea Johnson, his half-sister, who died in 1992 of pre-eclampsia.