There are 6 US Post Offices in Trinity County serving a total of 14,616 residents equating to 2,436 residents per post office. It's estimated that approximately 23,329 packages are handled across the 6 county post offices annually. Trinity County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 14,585. Its county seat is Groveton. The county is named for the Trinity River. Trinity County is included in the Huntsville, TX Micropolitan Statistical Area, which is also included in the Houston-The Woodlands, TX Combined Statistical Area.