There are 8 US Post Offices in Kittitas County serving a total of 40,347 residents equating to 5,043 residents per post office. It's estimated that approximately 64,398 packages are handled across the 8 county post offices annually. Kittitas County /\u02c8k\u026at\u1d7bt\u00e6s/ is a county located in the U.S. state of Washington. As of the 2010 census, the population was 40,915. Its county seat and largest city is Ellensburg. The county was created on November 24, 1883 when it separated from Yakima County. There are numerous interpretations of the name, which is from the language of the Yakama Nation. According to one source, it \"has been said to mean everything from 'white chalk' to 'shale rock' to 'shoal people' to 'land of plenty'. Most anthropologists and historians concede that each interpretation has some validity depending upon the particular dialect spoken.\" Kittitas County comprises the Ellensburg, WA Micropolitan Statistical Area."