The Mason-Dixon Line, named for Charles Mason and Jeremiah Dixon, the men who surveyed boundaries between Maryland and Pennsylvania, is known as the dividing line between the North and the South. But at the time of the survey, Delaware was part of Pennsylvania, known as the “Three Lower Counties.” So, the Mason-Dixon line runs along the southern border of Pennsylvania and turns south at Delaware. Since the southern border of Delaware was completed by other surveyors, it is not part of the Mason-Dixon line and that means Delaware is actually east of the colonial property line first established in the 1760s.
When Pennsylvania abolished slavery, it became known as the boundary between free states in the north and the southern states favoring the enslaving of human beings. Enslaved people who escaped captivity in southern states had a better chance at freedom if they could pass the Mason-Dixon Line into the north.
As a border state, Delaware became a bridge to freedom. It was not a safe bridge since slavery was still legal in the state. The Underground Railroad Byway begins where the Maryland byway ends on Willow Grove Road in Kent County. The route continues to Camden and Dover, passing through Smyrna, Middletown and Odessa. It then follows the Delaware River through New Castle to Wilmington and ends at the Delaware-Pennsylvania state line.
What is now known as the Mason-Dixon Line originated as a land survey to settle border disputes between the Penns of Pennsylvania and the Calverts of Maryland, it became known as the Mason-Dixon Line during the debates for the Missouri Compromise in 1820. Now associated with free states and slave states, it became popular in common thought as the boundary between the North and the South. While the border state of Maryland is definitively below the line, it never left the Union during the Civil War, although slavery remained legal until 1864. Similarly, Delaware was a border state with legal slavery, but it is east of the Mason-Dixon line.
Interestingly, the border surveyed by Mason and Dixon, when coupled with the 12-mile circle that originates from New Castle to form the northern border of Delaware, created the new issue of The Wedge where the lines did not match up. But that is a story for a later time.