The survey of what would eventually become the Mason-Dixon Line began in the 1680s, when surveyor Thomas Holme was appointed Surveyor General by William Penn. Holme was given the task of surveying the boundary between Pennsylvania and Maryland The original patent granted to Lord Baltimore (Cecilius Calvert, 2nd Baron Baltimore)set the boundary between Pennsylvania and Maryland at forty degrees north. The degree of latitude marking the division traced from a circle twelve miles north of Newcastle, Delaware, became the central issue in the dispute between Penn and Baltimore. Two groups of commissioners (one for each province) were appointed to mediate the resurvey of the line between Pennsylvania and Maryland, a process which lasted nearly forty years.
Over the decades-long process, several different surveyors were assigned to the project. In 1763, Charles Mason and Jeremiah Dixon, both Londoners, were commissioned to finish the survey. Charles Mason worked as assistant observer at the Royal Greenwich Observatory in London. Jeremiah Dixon was employed as a surveyor, and had worked previously with Mason.
The duo arrive in Philadelphia on November 15, 1763, at a time when there were still numerous conflicts between settlers and American Indians. Their goal was to complete the remainder of the survey in southeastern Pennsylvania and what is now northern Delaware, which they did using some of the most technologically-advanced instruments at their disposal, including telescopes, quadrants, and precision clocks. The final surveys were completed in the summer of 1768. Both Mason and Dixon returned to England afterwards, and they never again worked together. Dixon stayed in England, became a member of the Royal Society, and died in 1779. Mason, however, eventually returned to Philadelphia in the summer of 1786 with his family. Unfortunately, his stay was short lived as he died on October 25 of that same year. He was laid to rest in the Christ Church burial ground.
At HSP are the Mason-Dixon Line papers (Am .233), a small collection of documents relating to the survey. A number of our larger collections contain papers on the history of the survey as well, such as the Penn family papers (#485A) and the Chew family papers. (#2050).
Image: A Map of parts of the Provinces of Pensilvania [Pennsylvania] and Maryland with the Counties of Newcastle, Kent, and Sussex on Delaware according to the most exact Surveys yet made drawn in the year 1740