There are 5 US Post Offices in Franklin County serving a total of 77,434 residents equating to 15,487 residents per post office. It's estimated that approximately 123,593 packages are handled across the 5 county post offices annually. Franklin County is a county located in the U.S. state of Washington. As of the 2010 census, its population was 78,163. The county seat and largest city is Pasco. The county was formed out of Whitman County on November 28, 1883 and is named for Benjamin Franklin. Franklin County is included in the Kennewick-Richland, WA Metropolitan Statistical Area."