Mount Vernon is a city in Knox County, Ohio, United States, and its county seat. It is located along the Kokosing River, 40 miles (64 km) northeast of Columbus. The population was 16,956 at the 2020 census.

The community was platted in 1805, and named after Mount Vernon, the estate owned by George Washington.

In May 1953, the telephone exchange for the entire city was destroyed by fire, disrupting calls for months.

In January 1959, a severe flood caused 500 homes to be evacuated and caused $5 million in damage.

The Woodward Opera House, the oldest opera theater of its kind in the United States, is located downtown. The theater, after many years of renovation and restoration, has been transformed into a local cultural and performing-arts center.

The Knox County Historical Society, with a building and extensive exhibits, makes its headquarters on Harcourt Road in Mount Vernon. Exhibits feature information about Daniel Decatur Emmett, Paul Lynde, The Cooper Company and other subjects.

According to the United States Census Bureau, the city has a total area of 9.60 square miles (24.86 km²), of which 9.41 square miles (24.37 km²) is land and 0.19 square miles (0.49 km²) is water. The city lies in the Glaciated Allegheny Plateau and is surrounded by rolling hills and valleys.

The Kokosing River and U.S. Route 36 pass through the city.