Patrick Cassidy was born in the year 1738 in the village of Newry in County Down, Ireland. He emigrated to the English Colonies in 1752 while serving a British army officer. He learned the trade of surveying and participated as a surveyor in Forbe's Expedition to take Fort Duquesne in 1758. Prior to 1770 Patrick Cassidy married Mary Mooney. They gave birth to ten children.Cashada and Patrick Cassaday. The name, Patrick Casidy was recorded on the roster of Captain John Cobea's Company in May 1780, after the death of Captain Ashmead. In 1786 or 87, the name of Patrick Caseday was recorded as an ensign in Captain John Hollady’s Company, the 5th Company of the Bedford County Militia. In 1779 Patrick Cassidy was residing in Dublin Township, Bedford County, a region that would, in 1850, become part of Fulton County, Pennsylvania. After the American Revolutionary War, Patrick Cassidy continued in the profession of surveyor. His attention was turned to surveying and laying out towns. In the frontier of Cumberland, then Bedford, County Cassidy surveyed the towns of Hollidaysburg and Williamsburg. He is best known for having surveyed and laid out the village of Newry, named for his hometown in Ireland. Patrick Cassidy died on 17 July 1827 and was buried in the St. Patrick's Church (Catholic) Cemetery in Newry.
