Mount Vernon is a city in and the county seat of Posey County, Indiana, United States, in the state's far southwestern corner. The population was 6,687 at the 2010 census. It is located in Black Township and is part of the Evansville, Indiana, metropolitan area, which had a 2000 population of 342,815.
Mount Vernon is the county seat and largest city in Posey County, named for General Thomas Posey, Governor of the Indiana Territory, who had the distinction of growing up next door to George Washington at the original Mount Vernon, and who was widely rumoured to be Washington's illegitimate son. The rumors were dismissed by Posey's biographer, John Thornton Posey.
From around 1805 to 1816, Mount Vernon was known as McFadden's Bluff named for one of the first settlers to the area. There are a number of historic sites in Mount Vernon, including the Posey County Courthouse Square, Downtown Historic District, Welborn Historic District and the William Gonnermann House, all of which have been placed on the National Register of Historic Places.
The town has become a big center for plastics, with the manufacture of Lexan taking place just south of town at the SABIC plant; in addition, Port of Indiana-Mount Vernon, is an important part of the city's industry.