Fort Bosley was a grist mill located at the forks of the Chillisquaqua River at Washingtonville, Pennsylvania, that was fortified in 1777 during the American Revolution.

The gristmill was built in about 1773 by John Bosley, who moved to the area from Maryland a few years before the American Revolution. For early settlers in the region, hostilities with Native Americans were commonplace, intensifying after the outbreak of the Revolutionary War.

After General George Washington’s defeat at the Battle of Brandywine, leaders decided to develop a system of forts in the Susquehanna River Valley to protect settlers and support the defense of Fort Augusta. About a dozen forts were then established along the branches of the Susquehanna River, including Bosley’s Mill, which was fortified and stockaded in 1777.

It became a haven for area families while their husbands and fathers fought in the war. It was soon recognized by the military authorities as an important post and was garrisoned by troops. After the fall of Fort Freeland in July 1779, the fort became even more important, holding the forks of the Chillisquaqua River and defending the stream below it. During its tenure, no records show any attacks.

John Bosley sold his mill and surrounding land in 1795. It burned down in 1826, and no evidence of the mill exists today. A historical marker along Route 54 in Washingtonville, Pennsylvania.

 

©Kathy Alexander/Legends of America, updated November 2026.

Also See:

American Forts Photo Gallery

American Revolution

Forts & Presidios Across America

Pennsylvania Forts

See Sources.