The New York Times reviewed records for 50 of the largest Immigration and Customs Enforcement facilities and found detainees were kept in isolation for their own protection or for breaking facility rules.
The records did not detail the reasons individuals were placed in solitary, but human rights activists told the newspaper the practice amounted to abuse since the inmates face civil rather than criminal charges.
"I.C.E. is clearly using excessive force, since these are civil detentions," said Dr. Terry Kupers, a psychiatrist who studies solitary confinement at California's Wright Institute. "And that makes this a human rights abuse."
Approximately half of those in solitary were held for 15 days or more, which psychiatric experts consider the limit before mental health begins to suffer. About 35 were held for more than 75 days.
The Times said the 300-per-day average amounts to about 1 percent of the immigrants detained on a given day. Sources said it appeared about two-thirds of the detainees were locked up for disciplinary reasons. The others were isolated for their own protection because they were homosexual or mentally ill.
A spokeswoman for I.C.E. said placing inmates in solitary was a "last resort" for facility guards. "I.C.E. takes the mental healthcare of individuals in the agency's custody very seriously," she said.