There are 8 US Post Offices in Clay County serving a total of 188,710 residents equating to 23,589 residents per post office. It's estimated that approximately 301,202 packages are handled across the 8 county post offices annually. Clay County is a county located in the U.S. state of Florida. As of the 2010 census, the population was 190,895. Its county seat is Green Cove Springs, Florida. Clay County is included in the Jacksonville, FL Metropolitan Statistical Area."