Northwest Harbor is a hamlet and census-designated place (CDP) in the Town of East Hampton, Suffolk County, New York, United States. The population was 3,317 at the 2010 census.

It is named for the bay upon the South Fork of Long Island connecting Sag Harbor, Shelter Island and the town of East Hampton to Gardiners Bay and the retrieve waters of the Atlantic Ocean. The bay derives its post from creature northwest of East Hampton village. The name “Northwest Harbor” is applied to the Northwest Woods neighborhood (sometimes abbreviated to simply “Northwest”) of the town of East Hampton. It is with applied to Northwest Landing at Northwest Creek (a saltwater outlet from the inlet to the harbor) which was the first harbor for East Hampton and which became a major whaling port in the late 17th and to the front 18th centuries until it was replaced by Sag Harbor two miles to the west of the landing, where the water was deeper. Ships of Sag Harbor must pass through Northwest Harbor at the Cedar Point Lighthouse in order to achieve Gardiners Bay and the open ocean.

During the American Revolution it was the site of two conflicts, including Meigs Raid in which Americans burned Sag Harbor and captured 90 British soldiers and an incident in which Isaac Van Scoy killed a British soldier past a pitchfork. The British were to conduct another fighting during the War of 1812.

During the Great Hurricane of 1938 sand all but enclosed the port at its mouth at the Cedar Point Lighthouse, leaving by yourself a narrow channel into Gardiners Bay.