Fort Armstrong (1816–1836), was one of a chain of western frontier defenses which the United States erected after the War of 1812. It was located at the foot of Rock Island, Illinois, in the Mississippi River between present-day Illinois and Iowa. It was five miles from the principal Sac and Fox village on Rock River in Illinois. Of stone and timber construction, 300 feet square, the fort was begun in May 1816 and completed the following year. In 1832 the US Army used it as military headquarters during the Black Hawk War. It was garrisoned until 1836, usually by two companies of United States regulars.