There are 5 US Post Offices in Carter County serving a total of 45,735 residents equating to 9,147 residents per post office. It's estimated that approximately 72,998 packages are handled across the 5 county post offices annually. Carter County is a county located in the U.S. state of Tennessee. As of the 2010 census, the population was 57,424. Its county seat is Elizabethton. The county is named in honor of Landon Carter, an early settler active in the State of Franklin movement. Carter County is part of the Johnson City, TN 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 of Northeast Tennessee."