Harmar is a historic neighborhood in the city of Marietta, Ohio, United States. Located at the western side of the confluence of the Muskingum and Ohio Rivers, it grew up around the early Fort Harmar in the 1780s, being settled in conjunction with Marietta. After a period of forming part of Marietta, it existed separately beginning in 1837 before rejoining the …Harmar is a historic neighborhood in the city of Marietta, Ohio, United States. Located at the western side of the confluence of the Muskingum and Ohio Rivers, it grew up around the early Fort Harmar in the 1780s, being settled in conjunction with Marietta. After a period of forming part of Marietta, it existed separately beginning in 1837 before rejoining the mother city in 1890. Connected by bridge to the rest of the city, it retains much of its nineteenth-century architecture and landscape, and most of the neighborhood is now a historic district on the National Register of Historic Places.