There are 16 US Post Offices in Whitman County serving a total of 44,384 residents equating to 2,774 residents per post office. It's estimated that approximately 70,842 packages are handled across the 16 county post offices annually. Whitman County is a county located in the U.S. state of Washington. As of the 2010 census, the population was 44,776. The county seat is Colfax, and its largest city is Pullman. The county was formed out of Stevens County on November 29, 1871. It is named after Marcus Whitman, a Presbyterian missionary who, with his wife Narcissa, was killed in 1847 by members of the Cayuse tribe. Whitman County comprises the Pullman, WA Metropolitan Statistical Area."