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Before the Mason-Dixon Line was established, around 1690-1730, part of present-day Washington Boro was considered to be within the boundaries of Colonial Maryland. The Penn family didn’t quite agree. Maryland’s Charles Calvert, 5th Baron Baltimore held firm. This disagreement, which came to be known as Cresop’s War (or, the Conjocular War), lasted eight years and was, at times, quite bloody—so much so that the British crown had to step in to restore some semblance of peace. 

The conflict developed due to the less-than-precise boundary definition. It began by stating that Pennsylvania’s southern border should be a circle drawn at 12-miles distance from the center of New Castle (Delaware), northward and westward unto the beginning of the 40th degree of northern latitude, and then by a straight line westward. Confusing, right? To make matters worse, the gentleman who surveyed the area goofed, since the 40th parallel was, in fact, north of Philadelphia—placing Philadelphia well within Maryland, not Pennsylvania. Little wonder both sides were confused and both sides wanted the border to benefit their interests. 


Maryland clearly saw themselves as commanding the land northward to the 40th parallel—the initial agreement did state it as such, after all—which placed it running through the middle of present-day Washington Boro. The British crown insisted they work it out like gentlemen but Pennsylvania wasn’t buying it and proceeded to create Lancaster County, extending it south into land claimed by Maryland.

Calvert secured a land agent, Thomas Cresap, who worked for him to establish a settlement on the disputed land and set up shop in the vicinity of present-day Long Level Marina, where he ran Blue Rock Ferry (most likely named after the general area near our Center). During his operation, Cresap named the cluster of islands nearby, The Isles of Promise, which we call the Conejohela Flats.


In 1736, the situation came to a boil. Pennsylvania accused Cresap of murder, captured him and burnt his house down. Years later, King George II told both parties to fix the situation or he’d fix it for them. It took some time but they finally settled their differences. By 1767, Charles Mason and Jeremiah Dixon had been hired by the Penn and Calvert families to draw a line and they’d abide by it. 

Charles Calvert

5th Lord Baltimore

Proprietary Governor of Maryland

Thomas Penn

(son of William)

Proprietor of Pennsylvania

George II

King of Great Britain & Ireland

Prince-elector of the Holy Roman Empire

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