Newly obtained data show that about 80 percent of the 71,000 mostly Central American minors who crossed the U.S. border in 2014 were placed by the government with adults or sponsors who were in the country illegally.
The Department of Health and Human Services provided data in response to a Freedom of Information Act request by the Associated Press.
The data also show that six percent were placed with adults with temporary protected status, which applies to some Central American citizens who have been victims of a catastrophe. Four percent were sponsored by American citizens and 1 percent by immigrants facing deportation proceedings.
Many of the others were placed with sponsors who had other forms of legal status or who have filed immigration applications.
Tens of thousands of children from El Salvador, Guatemala and Honduras began arriving on the border in Texas in 2014, overwhelming border officials, overflowing government shelters and further backlogging the country's immigration courts.
Once apprehended by border agents, the children were placed in the care of Health and Human Services until caseworkers could screen and select suitable sponsors for them.
Republican lawmakers have blamed the influx on Obama administration policies they say encourage kids to leave their countries and come to the border. They say releasing unaccompanied children to sponsors who lack legal papers encourages illegal immigration and reduces the chances the children will show up for deportation hearings in immigration court.
Immigrant advocates insist the minors are fleeing violence and should be granted asylum. The top priority for children, they say, is to be placed with parents or close relatives so they can get on stable footing in the U.S. Any effort to deport sponsors might spook them from coming forward and put the children at risk.
Immigration status is not a factor in determining whether someone can sponsor a child. But sponsors are asked their status, and those in the country illegally must provide a backup plan to care for the children if they are deported.
U.S. House Judiciary Committee Chairman Bob Goodlatte, a Virginia Republican, said he was not surprised by the data. He blamed current policies for the surge on the border, but did not say whether placing children with sponsors who are here illegally created any additional problems.
"Since the president refuses to enforce our immigration laws, unlawful immigrants in the United States consistently pay criminal organizations along the border thousands of dollars to smuggle their family members into the United States," he said in a statement.
Rep. Zoe Lofgren, a Democrat from California and a Judiciary Committee member, said the government's responsibility is to find a safe home and guardian for children. Immigration status shouldn't matter, she said.
"If you were here as a legal resident or a U.S. citizen, you would petition for your child," she said. "Their only route is political asylum. It is not the visa system."
During the 20-month period covered by the data, more than half of unaccompanied children were released to a parent. Many others were placed with siblings, aunts and uncles.
Potential sponsors must provide proof of identity and their relationship to the child and undergo screening and background checks. In some cases, the department's Office of Refugee Resettlement conducts a home study to determine if the placement is safe.
The office has collected information about sponsors' immigration status since at least 2005, the Department of Health and Human Services said in a statement. Sponsors who are not the children's parents also are fingerprinted.
"The safety and well-being of every child in our care is of paramount importance at every stage," the statement said.
The statistics were culled from a database created in January 2014, according to the department.
Geyso Lemus from El Salvador said she didn't know what would happen to her 10-year-old son when he landed at a shelter in Illinois in 2014 because she didn't have legal papers, but a government social worker quickly put her at ease.
Two weeks later, she said, her son was sent to live with her in Southern California. He has since been granted asylum.
Based on reporting by the Associated Press.