On March 30, 1904, Hillman Post Office opens within the future city limits of Seattle. Martin Coltenbaugh is appointed postmaster. Hillman City is part of the Rainier Valley and is located four miles southeast of downtown Seattle.
The post office may have been located near the corner of Rainier Avenue S and S Orcas Street. Its name changed to Hanford Post Office on May 4, 1906.