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Mason-Dixon Line

the line that supposedly divides North from South

In 1632, King Charles I of England gave the first Lord Baltimore, George Calvert, the colony of Maryland. In 1682, King Charles II gave William Penn the territory to the north, which later became Pennsylvania. A year later, Charles II also gave Penn land on the Delmarva Peninsula. It was this last grant that led to what is now known as the Mason-Dixon Line (or Mason and Dixon's Line).

According to the original charters, the boundary between Maryland and Pennsylvania was supposed to be along 40 degrees north, but that line had never been formally "drawn." The addition of what is now Delaware to Penn's colony added extra confusion to the boundary question, and the Calvert and Penn families asked the British court to resolve the issue. In 1750, England's chief justice declared that the boundary between Pennsylvania and Maryland ran west and south from a point 15 miles south of Philadelphia. Ten years later, the two families agreed on the compromise and to have the boundary surveyed. America had no surveyors capable of taking on this task, however, so the Calverts and Penns agreed to hire two men from England.

Charles Mason and Jeremiah Dixon arrived in Philadelphia in November 1763. Mason was an astronomer who had worked at the Royal Observatory at Greenwich and Dixon was a renowned surveyor. They precisely established the point fifteen miles south of Philadelphia from which the boundary was to be drawn and erected a limestone benchmark. After establishing the line between Maryland and Delaware they began working their way west along the Maryland-Pennsylvania border. The men had been hired to "draw" the boundary for a distance of five degrees of longitude west from the Delaware River, but on October 9, 1767 their Iroquis guides refused to go any further because they had reached the border of their lands with the Lenape, with whom they were engaged in hostilities. The team made their final observations on October 11, 233 miles from its starting point, but 36 miles away from their intended end point. Their survey was officially received and accepted by the Penn and Calvert families on October 18.

one of the original crownstones set by Mason and Dixon
one of the original crownstones set by Mason and Dixon

The line drawn by Mason and Dixon remained nothing more than the Pennsylvania-Maryland-Delaware boundary until 1820, when the Missouri Compromise established a boundary between the slave states of the south and the free states of the north. That boundary became referred to as the Mason-Dixon line because it began in the east along the Mason-Dixon line and headed westward to the Ohio River and along the Ohio to its mouth at the Mississippi River and then west along 36 degrees 30 minutes North.

map of the Mason-Dixon Line
map of the Mason-Dixon Line

Aside from its completion to the western border of Pennsylvania, the Mason-Dixon line has not been changed since its first drawing. The tools Mason and Dixon were crude compared to the surveying technology of today, but modern technology has found their line to be remarkably accurate. Although many of the original marker stones were removed by locals and souvenir hunters over the subsequent years, a great many still stand; many of the ones stolen in years past have also been recovered and placed back in their original locations.

King Charles I
King Charles II
William Penn
Missouri Compromise

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The Robinson Library >> Middle Atlantic States >> General History and Description

This page was last updated on June 09, 2018.