There are 3 US Post Offices in Castro County serving a total of 7,396 residents equating to 2,465 residents per post office. It's estimated that approximately 11,805 packages are handled across the 3 county post offices annually. Castro County is a county located in the U.S. state of Texas. As of the 2010 census, its population was 8,062. The county seat is Dimmitt. The county was named for Henri Castro, who was consul general to France for the Republic of Texas and the founder of a colony in Texas. The county was originally created in 1876. It was organized in 1891, and a courthouse was built about the town square. Temporary county office space, meanwhile, was obtained from businessman J.N. Morrison. The ornate two-story courthouse was completed but was destroyed by lightning in 1906."