Editing Arthur St. Clair (section)

==Settler in America==
On April 16, 1762, St. Clair resigned his commission, and by 1764 had settled in [[Ligonier Valley, Pennsylvania|Ligonier Valley]], Pennsylvania, where he purchased land and went into business as an operator of flour and grist mills. The fortune he amassed soon made him the largest landowner in [[Western Pennsylvania]].

In 1770, St. Clair entered politics when he was elected as a justice of both the Court of Quarter Sessions and of Common Pleas. He subsequently served as a member of the proprietary council, a justice, recorder, and clerk of the orphans' court, and [[prothonotary]] of [[Bedford County, Pennsylvania|Bedford]] and [[Westmoreland County, Pennsylvania|Westmoreland]] counties.

In 1774, during [[Lord Dunmore's War]], the [[colony of Virginia]] illegally took claim of the area around present-day [[Pittsburgh, Pennsylvania|Pittsburgh]]. A militia was quickly raised to drive off the Virginians and St. Clair, in his capacity as a magistrate, issued an order for the arrest of the officer leading the Virginia troops. The boundary dispute between Virginia and Pennsylvania wasn't settled until 1780, when both sides agreed to extend the [[Mason–Dixon line]] westward from Maryland to 80° 31′ west, the current western border of Pennsylvania. (see: [[District of West Augusta]])