1779, named for Charles Mason and Jeremiah Dixon, English astronomers who surveyed (1763-7) the disputed boundary between the colonial holdings of the Penns (Pennsylvania) and the Calverts (Maryland). It became the technical boundary between "free" and "slave" states after 1804, when the last slaveholding state above it (New Jersey) passed its abolition act. As the line between "the North" and "the South" in U.S. culture, it is attested by 1834.
A boundary line between Pennsylvania and Maryland, laid out by two English surveyors, Charles Mason and Jeremiah Dixon, in the 1760s. Before and during the Civil War, the line was symbolic of the division between slaveholding and free states. After the war, it remained symbolic of the division between states that required racial segregation and those that did not.
Part of the boundary between Pennsylvania and Maryland established by the English surveyors Charles Mason and Jeremiah Dixon in the 1760s. The line resolved disputes caused by unclear description of the boundaries in the Maryland and Pennsylvania charters.
Note: Though the line did not actually divide North and South, it became the symbolic division between free states and slave states. Today, it still stands for the boundary between northern and southern states.