There are 3 US Post Offices in Unicoi County serving a total of 18,492 residents equating to 6,164 residents per post office. It's estimated that approximately 29,515 packages are handled across the 3 county post offices annually. Unicoi County is a county located in the U.S. state of Tennessee. As of the 2010 census, the population was 18,313. Its county seat is Erwin. Unicoi is a Cherokee word meaning \"white,\" \"hazy,\" \"fog-like,\" or \"fog draped.\" Unicoi County is part of the Johnson City Metropolitan Statistical Area, which is a component of the Johnson City\u2013Kingsport\u2013Bristol, TN-VA Combined Statistical Area, commonly known as the \"Tri-Cities\" region."