There are 9 US Post Offices in Sweetwater County serving a total of 43,439 residents equating to 4,827 residents per post office. It's estimated that approximately 69,333 packages are handled across the 9 county post offices annually. Sweetwater County is a county located in the U.S. state of Wyoming. As of the 2010 census, the population was 43,806. Its county seat is Green River. In area, it is the largest county in the state. It is in the southwestern part of Wyoming, north of the Colorado-Utah state line. Sweetwater County comprises the Rock Springs, WY Micropolitan Statistical Area."