Martins Ferry is the most populous city in Belmont County, Ohio, United States. The population was 6,260 as of the 2020 census. Located along the Ohio River across from Wheeling, West Virginia, it is part of the Wheeling metropolitan area.

Belmont County is a county in the U.S. state of Ohio. As of the 2020 United States census, the population was 66,497. Its county seat is St. Clairsville, while its largest city is Martins Ferry. The county was created on September 7, 1801, and organized on November 7, 1801. It takes its name from the French for "beautiful mountain".