Charters granted to colonies in Colonial America were based on inaccurate maps by people with little knowledge of the land, an issue that often led to property disputes between colonies. One such dispute, concerning the borders between Maryland (granted to Lord Baltimore), Pennsylvania (granted to William Penn), and Delaware (administered by the New York colony after the removal of the Dutch by force), was settled after over 100 years of litigation in the High Court Chancery in London. 

The settlement of the legal disputes resulted in the hiring of astronomer Charles Mason and surveyor Jeremiah Dixon in 1763. Between 1763 and 1767, Mason and Dixon walked the border between Maryland-Pennsylvania and Maryland-Delaware, leaving a marker at each mile along the way. (Though the original purpose of this survey was to settle the property dispute, the Mason-Dixon line became better known as the boundary between the Southern states where slavery was legal and Northern states where the slave trade had been prohibited.)

The Delaware-Maryland-Pennsylvania Tri-State Point sits at the northwestern corner of Delaware, the northeastern corner of Maryland, and the southern edge of Pennsylvania. Originally, a wooden marker was placed in 1765 by Mason and Dixon. It was replaced with a sturdier stone marker in 1849.

You can still find other markers along the Delware-Pennsylvania state line. Even after Mason and Dixon’s survey, border disputes between the two states continued until 1921 over a small area known as “the Wedge.”