Farmer's Castle was a defensive fortification built opposite the mouth of the Little Kanawha River on the Ohio River by a group of pioneers from the Ohio Company of Associates. It was located about 15 miles downriver of Marietta, Ohio, the first European-American settlement in the Northwest Territory. The pioneers had surveyed the land during the winter of 1788-89, and moved from Marietta to their new farms in April 1789. They called their town Belle-prairie, or modern day Belpre, Ohio. Adjacent to the island later known as Blennerhasset Island, the settlers began construction of Farmer's Castle during January 1791 for protection during the Northwest Indian War.