Mary Armstrong was the daughter of William Armstrong and Jean. William Armstrong with his two brothers John and George and sister Margaret emigrated from the north of Ireland and settled in Carlisle, Pennsylvania sometime before the year 1748. "William Armstrong's Settlement" was on the Conodoguinet just below the Meeting House Springs. Mary Armstrong married Robert Sanderson. Their children were George, Robert, John, Alexander, William, Martha and Jane Sanderson. Mary was also buried in the old graveyard adjoining their farm.