There are 4 US Post Offices in Calhoun County serving a total of 21,349 residents equating to 5,337 residents per post office. It's estimated that approximately 34,075 packages are handled across the 4 county post offices annually. Calhoun County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 21,381. Its county seat is Port Lavaca. The county is named for John Caldwell Calhoun, the seventh vice president of the United States. Calhoun County comprises the Port Lavaca, TX Micropolitan Statistical Area, which is also included in the Victoria-Port Lavaca, TX Combined Statistical Area.