There are 5 US Post Offices in Maries County serving a total of 7,638 residents equating to 1,528 residents per post office. It's estimated that approximately 12,191 packages are handled across the 5 county post offices annually. Maries County is a county located in the U.S. state of Missouri. As of the 2010 census, the population was 9,176. Its county seat is Vienna. The county was organized March 2, 1855 and named for the Maries River and Little Maries River. 'Maries' is derived from the French marais, which means marsh, lake or pond.