The Arsenal was built circa 1809 in Watertown, New York.
By an act of the Legislature in 1808, five hundred stand of arms were ordered to be stored or deposited at Champion, but in a little time these arms were ordered to Watertown, and also an Arsenal was planned and was soon in process of construction on the east side of Arsenal street. [Source]
During the war of 1812, Watertown was often excited and made anxious by its proximity to Sackett's Harbor, an important naval station of the government and the scene of one or two spirited battles.
During the war of 1812, bodies of troops were stationed at Watertown for short periods, and the sick were often sent here from Sackett's Harbor for better attendance than could be had there. [Source]