There are 24 US Post Offices in Placer County serving a total of 247,841 residents equating to 10,327 residents per post office. It's estimated that approximately 395,582 packages are handled across the 24 county post offices annually. Placer County (/\u02c8pl\u00e6s\u0259r/ PLAS-\u0259r), officially the County of Placer, is a county located in the U.S. state of California. As of the 2010 census, the population was 348,432. The county seat is Auburn. Placer County is included in the Sacramento-Roseville-Arden-Arcade, CA Metropolitan Statistical Area. It is located in both the Sacramento Valley and Sierra Nevada regions, in what is known as the Gold Country. It stretches from the suburbs of Sacramento to Lake Tahoe and the Nevada border."