There are 5 US Post Offices in Duval County serving a total of 12,620 residents equating to 2,524 residents per post office. It's estimated that approximately 20,143 packages are handled across the 5 county post offices annually. Duval County is a county located in the U.S. state of Texas. As of the 2010 census, its population was 11,782. The county seat is San Diego. The county was founded in 1858 and later organized in 1876. It is named for Burr H. Duval, a soldier in the Texas Revolution who died in the Goliad Massacre."