The Hammonasset Paper Mill Site preserves the remains of a nineteenth-century paper mill complex along the Hammonasset River between Killingworth and Madison, Connecticut. Built in 1865 and operated until 1890, the mill used river water power and produced strawboard, a paper material once used for boxes before wood-pulp paper became common. Surviving ruins include part of a stone dam, the stone mill foundation, and raceways, and the site later served briefly as a lumber mill. In its wooded setting, the ruins remain a rare reminder of the small-scale industrial activity that once lined Connecticut rivers.