There are 3 US Post Offices in Harmon County serving a total of 2,867 residents equating to 956 residents per post office. It's estimated that approximately 4,576 packages are handled across the 3 county post offices annually. Harmon County is a county located in the southwest corner of the U.S. state of Oklahoma. As of the 2010 census, the population was 2,922, making it the second-least populous county in Oklahoma, behind only Cimarron County. It has lost population in every census since the first in 1910, except 1930. The county seat is Hollis.