Description: Fort Johnstown was built in the mid-1770s, in Johnstown, New York. The fortification surrounded a stone jail. The defensive structure was palisaded with blockhouses built upon diagonal corners. The fort served as a frontier jail and military prison during the American Revolution. Note from Adirondack Scenic Byways: "NYS road marker reads Third Mohawk Valley House Built By Sir William Johnson. Important Military Post and Indian Council Place of 1754 to 1760. Fort Johnstown’s heyday was between 1772 and 1776. A fortified stone jail that was palisaded with blockhouses at the diagonal corners, serving as frontier jail and military prison during the American Revolution. From downtown Johnstown and Route 30A north, turn west onto East Main Street, a.k.a. Routes 29 and 67, north onto North William Street, or Route 29, and then a right on Hall Avenue."