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History of the Mason-Dixon Line

written by: Bruno Kos • edited by: Noreen Gunnell • updated: 6/6/2012

What is the Mason-Dixon Line? Why was it drawn? Find the answers in this article.

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    In order to solve a border dispute between British colonies in Colonial America, two surveyors Charles Mason and Jeremiah Dixon mapped the line which eventually became known as the Mason-Dixon Line. Despite the fact that, during the 19th century, the line was usually identified as a division between the Northeastern United States and Southern United States, the line itself has roots in the mid-18th century.

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    Prior to considering crucial moments surrounding the creation of the Mason-Dixon Line, a few words should be mentioned regarding some events that occurred in the 17th century. The first important event occurred in 1632, when King Charles I of England assigned the colony of Maryland to George Calvert (who himself was the first Lord Baltimore). Further, in 1682, King Charles II of England (successor to King Charles I) assigned William Penn the territory which was north of Maryland (this area later became Pennsylvania). Finally, in 1683, King Charles II assigned William Penn land on the Delmarva Peninsula.

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    Boundary Problem

    The problem concerning the boundary was eventually raised. Families of Calvert and Penn were rather confused as to where the boundary lay. Since the families were unable to find an answer, they decided to let the British court handle the issue. The result was that in 1750, England's chief justice declared that the boundary between northern Maryland and southern Pennsylvania lay 15 miles south of the city of Philadelphia. Ten years later, both families decided to survey the new boundary. As there weren’t skilled people available, two surveyors from England were recruited; their names were Charles Mason and Jeremiah Dixon.

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    Charles Mason and Jeremiah Dixon - First Tasks Upon Arrival

    Charles Mason was an astronomer, working at the Royal Observatory at Greenwich. Jeremiah Dixon was a skilled surveyor, who had worked with Mason for many years prior to their arrival in Philadelphia in November, 1763. The first task upon arrival was the determination of the exact, absolute location of Philadelphia, as this was the point from which they would begin to survey the north-south line. This line divided the Delmarva Peninsula into the properties of the Penn and Calvert families. Once they completed the job, they started to mark the line running east-west, which divided Maryland and Pennsylvania.

    The first result of their work was a point located fifteen miles south of Philadelphia. Next, they started the measurements to the east of that point.

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    Final Solution

    Their further travels were rather difficult, as there were many dangerous situations they encountered. Some of their difficulties came from indigenous Native Americans, who lived in the regions where they were surveying. Eventually, the hostile residents were responsible for the surveyors not reaching their final goal. Finally, on October the 9th, 1767, the boundary had almost been completed; it was 233 miles long.

    Considering the information provided in this article, it is clear that the Mason-Dixon Line has roots which concern primarily geographical issues. However, despite this fact, the Line will always be somehow thought of as a boundary dividing freedom and slavery, rather than as both an historical and geographical demarcation.


  • John Davenport: The Mason-Dixon Line, Infobase Publishing, 2004.