Nantucket is an island south of Cape Cod, Massachusetts, in the United States. Together with the small islands of Tuckernuck and Muskeget, it constitutes the town of Nantucket, Massachusetts and the coextensive Nantucket County, which cover all three islands. The region of Surfside on Nantucket is the southernmost settlement in Massachusetts. Nantucket is a tourist destination and summer colony. The population of the island soars from approximately 10,000 to 50,000 during the summer months, due to tourists and summer residents. It has some of the highest property values in Massachusetts.

The National Park Service has designated the entire island as a National Historic District, paying particular note to the settlements of Nantucket and Siasconset. The island features one of the highest concentration of pre-Civil War structures in the United States.