There they set up a new milling business, founding the town of Ellicott's Mills in 1772 (today's Ellicott City, Maryland). Three years later, Andrew married Sarah Brown (1756/8–1827) of Newtown, Pennsylvania, with whom he would have ten children, one of which died as a child. When the Revolutionary War broke out in 1775, Andrew enlisted as a commissioned officer in the Elk Ridge Battalion of the newly organized Maryland state militia despite his Quaker upbringing. During the course of the war, he rose to the rank of major, a title he would keep as an honorific throughout his life.