The Boonsboro Historic District is historically significant for its association with the development of Western Maryland following the opening of the National Road in the early 19th century. The road linked rural Washington County with the port of Baltimore as well as points to the west, and was an important influence on the agricultural, economic, and commercial development of the region throughout the 19th century. Boonsboro's location along the National Road, adjoining Turner's Gap through South Mountain, was strategically important during the American Civil War, and throughout the conflict the town experienced the passage of thousands of troops and accommodated the wounded soldiers left to the care of townspeople. Its growth through the first half of the 20th century, associated with another transportation corridor, the Hagerstown-Boonsboro Electric Railway branch line, is clearly apparent in the architectural character of the areas that were annexed into the town during that period. The Boonsboro Historic District derives additional significance as an excellent example of a type of linear development characteristic of town plans in the region in the 19th century, and for the wide variety of architectural types and styles represented by its component buildings, which chronicle the town's development from its founding in 1792 through the mid 20th century. The period of significance, from 1792-1959 tracks the continuous growth and evolution of the town through the date by which the district had substantially achieved its current form and appearance.