There are 5 US Post Offices in Clatsop County serving a total of 35,452 residents equating to 7,090 residents per post office. It's estimated that approximately 56,585 packages are handled across the 5 county post offices annually. Clatsop County /\u02c8kl\u00e6ts\u0259p/ is a county located in the U.S. state of Oregon. As of the 2010 census, the population was 37,039. The county seat is Astoria. The county is named for the Clatsop tribe of Native Americans, who lived along the coast of the Pacific Ocean prior to European settlement. Clatsop County comprises the Astoria, OR Micropolitan Statistical Area."