The Trump administration has reunited 364 separated migrant children over the age of five with their families thus far, according to a new court filing.
Government lawyers also stated over 900 parents are "not eligible or not yet known to be eligible" for reunification.
Thursday's filing comes a week before the court-imposed reunification deadline.
Officials have identified 2,551 children to evaluate for reunification.
With only a week before the 26 July deadline, the Trump administration has reunited 14% of the migrant children who were separated from their parents at the US-Mexico border as a part of the "zero tolerance" immigration policy.
According to the filing, the government has deemed 1,606 parents as "possibly eligible" to be reunited with their children - of that total, they have cleared 848 parents, and 222 parents have been released.
Over 500 of these "possibly eligible" cases are still pending.
As of Thursday, 908 parents are still classified as "either not eligible or not yet known to be eligible for reunification".
The filing states that 136 parents had "waived reunification" during the interview process, and another 91 had a "prohibitive criminal record" or were "deemed ineligible by ICE [Immigration and Customs Enforcement]".
In all, the government will need to finish the evaluation or interview process for, at minimum, 1,200 parents by next week's deadline, according to the report.
The Trump administration has not commented on whether or not officials will meet that deadline.
The American Civil Liberties Union (ACLU) stated in the filing that the government has still not provided a list of parents who have been deported, released from ICE custody or have orders to leave the US immediately.
The ACLU also wrote on Thursday that the government has yet to clarify how parents of children under five - whose reunification deadline passed on 10 July - were deemed ineligible.
The government has said that all eligible children under the age five have now been reunited.
On Monday, Judge Dana Sabraw, the federal judge in charge of the migrant reunification process, ordered the government to stop deporting families after the ACLU expressed concerns over "mass deportations... carried out imminently and immediately upon reunification" that would prevent families from making asylum claims.
The ACLU has requested that migrant families have a week to decide how to proceed after being reunited.
During Monday's hearing, Jonathan White, a senior official from the Department of Health and Human Services, said that the government has not been able to find the parents of 71 children, US media reported.