There are 7 US Post Offices in Sevier County serving a total of 19,005 residents equating to 2,715 residents per post office. It's estimated that approximately 30,334 packages are handled across the 7 county post offices annually. Sevier County /s\u025b\u02c8v\u026a\u0259r/ is a county located in the U.S. state of Utah. As of the 2010 census, the population was 20,802. Its county seat and largest city is Richfield. The county was formed on January 16, 1865, as a split off from Sanpete County to the north. It was named for the nearby Sevier River."