Marietta is a city in Washington County, Ohio, United States, and its county seat. It is located in southeastern Ohio at the confluence of the Muskingum and Ohio Rivers, 11 miles (18 km) northeast of Parkersburg, West Virginia. As of the 2020 census, Marietta has a population of 13,385 people. It is the principal city of the Marietta micropolitan area, which includes all of Washington County, and is the second-largest city in the Parkersburg–Marietta–Vienna combined statistical area.
Founded in 1788 by pioneers to the Ohio Country, Marietta was the first permanent U.S. settlement in the newly established Northwest Territory, created in 1787, and what would later become the state of Ohio.