There are 11 US Post Offices in Clay County serving a total of 27,600 residents equating to 2,509 residents per post office. It's estimated that approximately 44,053 packages are handled across the 11 county post offices annually. Clay County is a county located in the U.S. state of Indiana. As of 2010, the population was 26,890. The county seat is Brazil. Clay County is included in the Terre Haute, Indiana, Metropolitan Statistical Area."