There are 10 US Post Offices in Sierra County serving a total of 19,118 residents equating to 1,912 residents per post office. It's estimated that approximately 30,514 packages are handled across the 10 county post offices annually. Sierra County is a county located in the U.S. state of New Mexico. As of the 2010 census, the population was 11,988. Its county seat is Truth or Consequences."