Penobscot Indian Island Reservation is an Indian reservation for the Penobscot Tribe of Maine, a federally recognized tribe of Penobscot tribe in Penobscot County, Maine, United States, near Old Town. The population was 610 at the 2010 census. The reservation extends for many miles alongside 15 towns and two unorganized territories in a thin string along the Penobscot River, from its base at Indian Island, near Old Town and Milford, northward to the vicinity of East Millinocket, almost entirely in Penobscot County. A small, uninhabited part of the reservation is in South Aroostook, Aroostook County, by which it passes along its way northward.