The Old King's Highway Historic District encompasses what was historically the principal east-west thoroughfare through Barnstable, Massachusetts. It encompasses Barnstable's entire length of what is now designated Massachusetts Route 6A and called Main Street, between the town lines of Sandwich and Yarmouth. It includes more than 1,000 acres (400 ha), and includes all of the buildings whose properties front on the road, nearly 500 in all. The area includes the main population centers of Barnstable from its founding in the late 1630s until the mid-19th century, when the southern parts of the community became more significant in economic prominence. The district was listed on the National Register of Historic Places in 1987.