In letters obtained by ABC7 I-Team through the Freedom of Information Act, ICE requested Sheriff Dart serve immigration subpoenas.
The federal agency said failing to serve them could result in prosecution for tampering with a witness.
The Cook County Sheriff's Office says it cannot release an individual in custody to any law enforcement agency or federal agents for an interview.
The sheriff's office also says three of the individuals named in the letters were released before the office received them.
ABC7 reached out to the U.S. Department of Homeland Security for comment but did hear back yet.