There are 13 US Post Offices in Plumas County serving a total of 18,548 residents equating to 1,427 residents per post office. It's estimated that approximately 29,605 packages are handled across the 13 county post offices annually. Plumas County is a county located in the Sierra Nevada of the U.S. state of California. As of the 2010 census, the population was 20,007. The county seat is Quincy, and the only incorporated city is Portola. The largest community in the county is East Quincy. The county gets its name from the Spanish words for the Feather River (R\u00edo de las Plumas), which flows through the county."