There are 3 US Post Offices in Gaines County serving a total of 16,825 residents equating to 5,608 residents per post office. It's estimated that approximately 26,855 packages are handled across the 3 county post offices annually. Gaines County is a county located in the U.S. state of Texas. As of the 2010 census, its population was 17,526. The county seat is Seminole."