There are 5 US Post Offices in Sherman County serving a total of 1,765 residents equating to 353 residents per post office. It's estimated that approximately 2,817 packages are handled across the 5 county post offices annually. Sherman County is a county located in the U.S. state of Oregon. As of the 2010 census, the population was 1,765, making it the second-least populous county in Oregon. The county seat is Moro, and the largest city is Wasco. The county is named for William Tecumseh Sherman, a Union general in the American Civil War.