There are 1 US Post Offices in Garfield County serving a total of 2,293 residents equating to 2,293 residents per post office. It's estimated that approximately 3,660 packages are handled across the 1 county post offices annually. Garfield County is a county located in the U.S. state of Washington. As of the 2010 census, the population was 2,266, making it the least populous county in Washington; with about 3.2 inhabitants per square mile (1.2/km2), it is also Washington's least densely populated county. The county seat and only city is Pomeroy.