Border Patrol Agents Detain Migrants Near US-Mexico Border MISSION, TX - JUNE 12: U.S. Border Patrol agents take into custody a father and son from Honduras near the U.S.-Mexico border on June 12, 2018 near Mission, Texas. The asylum seekers were then sent to a U.S. Customs and Border Protection (CBP) processing center for possible separation. U.S. border authorities are executing the Trump administration's zero tolerance policy towards undocumented immigrants. U.S. Attorney General Jeff Sessions also said that domestic and gang violence in immigrants' country of origin would no longer qualify them for political-asylum status. (Photo by John Moore/Getty Images)
Getty Images
Border Patrol Agents Detain Migrants Near US-Mexico Border MISSION, TX - JUNE 12: U.S. Border Patrol agents take into custody a father and son from Honduras near the U.S.-Mexico border on June 12, 2018 near Mission, Texas. The asylum seekers were then sent to a U.S. Customs and Border Protection (CBP) processing center for possible separation. U.S. border authorities are executing the Trump administration's zero tolerance policy towards undocumented immigrants. U.S. Attorney General Jeff Sessions also said that domestic and gang violence in immigrants' country of origin would no longer qualify them for political-asylum status. (Photo by John Moore/Getty Images)
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(CNN) —  

The Department of Health and Human Services will keep open and expand a temporary tent facility for immigrant children it is operating in Tornillo, Texas, even as most of the children it was caring for as a result of family separations at the border have been moved out of HHS custody.

According to HHS Administration for Children and Families spokesman Kenneth Wolfe, the facility will more than triple its capacity to 3,800 temporary bed spots and will stay open at least through December 31. Not all of the beds will come online at once – 1,400 of them will be placed on reserve to be opened as needed. The facility currently has 1,200 beds.

Wolfe said family separations were “not driving” the expansion, which is being done to accommodate the high number of children who came to the US illegally by themselves. There are more than 12,800 children currently in HHS custody, a number higher than many of the weekly totals during the family separation crisis this summer. Only about 400 of those children are considered separated from families.

“HHS is legally required to provide care and shelter for all unaccompanied alien children referred by DHS, and works in close coordination with DHS on the security and safety of the children and community,” Wolfe said in a statement.

It’s not clear why there is still such a high number of unaccompanied immigrant children in HHS’ care. Since a federal court ordered the administration to reunify all eligible separated families, more than 2,100 children have been released from custody either to their parents or other suitable adults. The Trump administration stopped separating families in order to prosecute the parents criminally on June 20.

For most of the year, roughly 3,000 to 4,000 children have come to the US illegally by themselves each month. In May and June, that number topped 6,000 and 5,000, respectively, but in July it was back under 4,000. August numbers have not been released yet. An HHS official, on the condition of anonymity, pointed to the forthcoming release of August figures from the Department of Homeland Security when asked to explain the high population.

HHS and the DHS have made a number of moves to more closely scrutinize adults who come forward to take the unaccompanied children out of custody, including a partnership to fingerprint and check the backgrounds of potential “sponsors,” as they’re called. But many of the relatives and even parents are themselves undocumented, and might balk at the prospect of a fingerprint check by Immigration and Customs Enforcement. Former acting ICE Director Tom Homan said last year that ICE would not hesitate to arrest undocumented immigrants who come forward as sponsors for unaccompanied children. The process to release a child was averaging nearly 60 days to complete as of this summer.

The Trump administration had selected the federal land in Tornillo in June to temporarily house unaccompanied immigrant children, as the agency sought more capacity amid the increasing number of families then being separated at the border.

The original Tornillo contract was set to run through July 13. There were initially just over 300 children there, mostly boys, few of whom had been separated from families.

An incident commander at Tornillo told reporters in June that “this operation would not be here if it weren’t for the separation.”

“I’m totally against the separation policy,” he added. “It’s an incredibly dumb, stupid decision made by our leadership.”

CNN’s Dianne Gallagher contributed to this report.