Considered a "dangerous enemy alien," Matahichi Iseri was separated from his family and sent to the Department of Justice internment camp at Fort Missoula, Montana. In June 1942, he received a Change of Residence Notice certificate, which indicated that his request to join his family at the Pinedale Assembly Center in California had been approved.

Matahichi Iseri was arrested on December 7, 1941, and taken to Fort Missoula, Montana, where he was detained at a Department of Justice internment camp for "enemy aliens." While he was separated from his wife and children, he was able to send a limited number of letters to them.