MASON-DIXON LINE is the southern boundary line of Pennsylvania, and thereby the northern boundary
line of Delaware, Maryland, and West Virginia, formerly part of Virginia. It is best known historically as the dividing line between slavery and free soil in the period of history before the Civil War, but to some extent it has remained the symbolic border line—political, cultural, and social—between North and South.
The present Mason and Dixon line was the final result of several highly involved colonial and state boundary disputes. The first dispute was between Maryland and Pennsylvania. The Maryland Charter of 1632 granted to the Calvert family lands lying north of the Potomac River and "under the fortieth degree of Northerly Latitude." Almost fifty years later (1681), Charles II issued a charter making William Penn proprietor of lands between latitudes 40° N and 43° N and running west from the Delaware River though five degrees in longitude. The terms of the two charters were inconsistent and contradictory. A full century of dispute with regard to the southern boundary of Pennsylvania was the result. Had all Pennsylvania claims been substantiated, Baltimore would have been included in Pennsylvania, and Maryland reduced to a narrow strip. Had all Maryland claims been established, Philadelphia would have been within Maryland.
In 1760, after years of conferences, appeals to the Privy Council, much correspondence, attempted occupation, forced removal of settlers, and temporary agreements, the Maryland and Pennsylvania proprietors reached an agreement to resolve the dispute. Under its terms, two English surveyors, Charles Mason and Jeremiah Dixon, surveyed the boundary line. In 1767, after four years' work, Mason and Dixon located the boundary line between Maryland and Pennsylvania at 39° 44' north latitude. The crown ratified the results in 1769.
In the meantime Virginia claimed most of what is now southwestern Pennsylvania. Both colonies tried to exercise jurisdiction in the area, which led to conflicts in 1774 and 1775. That dispute ended when joint commissioners of the two states agreed to extend the Mason and Dixon line westward, a settlement not completed until 1784. Historically the Mason-Dixon line embodies a Pennsylvania boundary triumph.
Buck, Solon J., and Elizabeth H. Buck, The Planting of Civilization in Western Pennsylvania. Pittsburgh, Pa.: University of Pittsburgh Press, 1939.
Danson, Edwin. Drawing the Line: How Mason and Dixon Surveyed the Most Famous Border in America. New York: John Wiley, 2001.
Illick, Joseph E. Colonial Pennsylvania: A History. New York: Scribners, 1976.
Morrison, Charles. The Western Boundary of Maryland. Parson, W. Va.: McClain Print Co., 1976.
Alfred P.James/c. p.