Sackett's Harbor (or more correctly Sack-et's), a village in the town of Hounsfield, Jefferson co., New York, on the S. shore of Black River bay, an inlet of Lake Ontario, at the terminus of the Utica and Black River railroad, 10 m. W. S. W. of Watertown; pop. in 1875, 734. The harbor, one of the best on the lake, is divided by a crescent-shaped tongue of land, which extends from the lower part of the village, into the outer and inner harbor. The latter has sufficient depth of water for large vessels to within two fathoms of the shore. Its commerce, formerly extensive, has been mostly diverted to other channels. The Madison barracks, built by the government in 1816-'19, at a cost of $85,000, are situated here. - In the war of 1812 Sackett's Harbor was the headquarters of the northern division of the American fleet, and several war vessels were built and expeditions fitted out here. It was twice attacked by the British, who were repulsed, the last time with a loss of 150 men.