Fort James: British renamed Fort Amsterdam. Fort James Aug 1664. Renamed Fort George between 1687-1703. Briefly reoccupied by the Dutch 1673-74 as Fort Willem Hendrick. Destroyed by Americans 1776.
Fort Jay: 1797, Governor's Island. First a battery in 1776, then garrisoned by British from 1776-1782. Fort Jay (for John Jay one-time Governor of NY) built 1797-98, upgraded in 1803 and renamed Fort Columbus 1803-1904. Reverted to Fort Jay.
Jersey Battery: One of the stronger forts in downtown Manhattan, close to the Hudson shore. To the left of Grenadier's Battery on line with present Reade Street west of Greenwich Street. Feb-May 1776, a five sided fortification with a line of entrenchments to Grenadier's. April 1776 along with Oyster Battery and Whitehall Battery engaged British Phoenix and Rose. British improved works 1782 during their occupation.
Fort Jersey: 1776, Delaware River at Mohochamack Fork. Blockhouse, two miles from the Minisink Forts and Port Jervis.
Fort Johnson: 1744-9, second fortified stone house built by Sir William Johnson on the Mohawk River. Residency during the French and Indian Wars. An earlier unfortified residence known as Mount Johnson was built near Amsterdam in 1739. This 12 mile square parcel was called "The Royal Grant." In 1755 also had palisade and two blockhouses.
Fort Johnstown: 1772-6, Johnstown. Fortification of stone jail. Palisaded with blockhouses at the diagonal corners. Served as frontier jail and military prison during the American Revolution. From: http://www.adirondackscenicbyways.org/resource/fort-johnstown-and-the-former-fulton-county-jail.html "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."
Joncaire's Blockhouse: 1719(21), Niagara Falls, Niagara County. Also known as Fort Joncaire, and Magazin Royal. Daniel Joncaire, French "white indian", built a stockaded cabin and warehouse for trading, in Lewiston at the foot of the portage (base of gorge) about 7 miles from the future Fort Niagara. Dedicated as Magazin Royal by Baron de Longueuil Lt Gov of Montreal. This may have been near the site of the original 1678 French Fort Hennepin, and a later unnamed storehouse in 1679. Later the British also had an unnamed storehouse/ Blockhouse on this location. Another fort was built by Joncaire in 1750 called Fort Little Niagara or Fort du Portage at the upper end of the portage above the falls (old upper camp of Fort Conti 1679).