There are 5 US Post Offices in Dallas County serving a total of 14,217 residents equating to 2,843 residents per post office. It's estimated that approximately 22,692 packages are handled across the 5 county post offices annually. Dallas County is a county located in the U.S. state of Missouri. As of the 2010 census, the population was 16,777. Its county seat is Buffalo. The county was organized in 1842 as Niangua County and then renamed in 1844 for George M. Dallas, who served as Vice President under James K. Polk. Dallas County is part of the Springfield, MO Metropolitan Statistical Area."