Knoxville is an unincorporated community in Frederick County, Maryland, United States. The Robert Clagett Farm and Magnolia Plantation are listed on the National Register of Historic Places.Knoxville is situated at the base of South Mountain directly beside the Potomac River to the immediate east of the water gap leading towards Harpers Ferry, West Virginia. The first settlers, English and German, began to populate the area in the latter half of the 18th century. By the early 19th century, a village began to form along the main road leading from Frederick, Maryland, to Harpers Ferry, the site of one of the two national armories in the United States. The coming of the Baltimore and Ohio Railroad, Chesapeake and Ohio Canal, and the establishment of the industrial town of Weverton to the immediate west fueled the growth of Knoxville in the 1840s.In 1849, the Frederick Examiner newspaper reported that Knoxville was flourishing with new businesses and houses.