There are 3 US Post Offices in Rockwall County serving a total of 50,845 residents equating to 16,948 residents per post office. It's estimated that approximately 81,154 packages are handled across the 3 county post offices annually. Rockwall County is a county located in the U.S. state of Texas. At 129 square miles, Rockwall County has the smallest area of any county in Texas. As of the 2014 census, its population was 87,809. Its county seat is Rockwall. The county and city are named for a wall-like subterranean rock formation that runs throughout the county. Rockwall County is part of the Dallas-Fort Worth-Arlington, TX Metropolitan Statistical Area. It was one of the top twenty-five fastest-growing counties in the U.S. in 2010. Rockwall County is currently listed as the 6th wealthiest county in Texas. Its cities include Rockwall, Royse City, Fate, McClendon-Chisolm, Mobile City, and a part of Rowlett."