A city and the county-seat of Knox county, Ohio, U.S.A., on the Kokosing river, about 45 m. N.E. of Columbus. Pop. (1890), 6027; (1900), 6633, of whom 359 were foreign-born and 239 were negroes. Mount Vernon is served by the Baltimore & Ohio and the Cleveland, Akron & Columbus, railways. The city is the seat of the state hospital for tuberculosis, has a fine court-house, a public library, and various manufacturing establishments. Natural gas is found in the vicinity. Mount Vernon was laid out in 1805; it became the county-seat in 1807, was incorporated as a town in 1845, and became a city in 1853.