The British maintained the fort until after the United States victory in the Northwest Indian War and the signing of Jay's Treaty in 1795.

After Great Britain defeated France in the Seven Years' War, the French transferred the fort to British forces, who occupied it in October 1761.

In 1780, a Patriot force from Cahokia, Illinois, led by Jean-Baptiste Hamelin and Lieutenant Thomas Brady, raided the fort, plundering its content and capturing several traders.

[citation needed] After the defeat of Hamelin's party, two Milwaukee chiefs, El Heturnò and Naquiguen, traveled to Spanish-held St. Louis; they arrived on 26 December 1780, to report the failed raid.

[6] When Cruzat wrote about it to Governor Gálvez, he justified the raid as needing to appear strong to his Native allies, and to forestall British actions in the region.

[9] Although Cruzat treated the raid as an act of Indian affairs, the looting and destruction of goods held at Fort St. Joseph also dissuaded a second British attack into Spanish territory.

[10] The British finally abandoned the fort after the United States victory in the Northwest Indian War and the signing of Jay's Treaty in 1795.

Based on its Fort St. Joseph expedition, Spain claimed lands east of the Mississippi River, but this was not recognized by the United States.

[11] Because of the long dispute over the land, the diplomats Benjamin Franklin and John Jay considered the Spanish campaign at Fort St. Joseph to have been little more than a ploy to claim the Northwest Territory.

They include "trade silver, musket parts, glass beads, buttons, gunflints, knife blades, and door hinges.

"[4] The specific location of the 15-acre fort site was forgotten, and part of it is likely underwater since a dam downriver raised the water level.

[12][13] Support the Fort, a local interest group founded in 1992, has helped sponsor a major archeological excavation on site, which began in 2002.

[15] In December 2010 the team made a critical find of a foundation wall and two wooden posts of one of the buildings, helping establish its scale.