Later years found him living in Hollywood and, by 1942, on his daughter's ranch outside Banning, California. Due to his age and health conditions, Hartmann was one of only a few Japanese Americans on the West Coast to avoid the mass incarceration during World War II, although the FBI and local officials visited the ranch often to conduct investigations.
As time went on, Hartmann settled in Hollywood, and by 1942, he had relocated to his daughter's farm outside Banning, California. His advanced age and health problems made him one of the few Japanese Americans on the West Coast who avoided being interned during World War II, although law enforcement officials and the FBI regularly visited the ranch for inquiries.