Penobscot Indian Island Reservation is an Indian reservation for the Penobscot Tribe of Maine, a federally recognized tribe of the Penobscot in Penobscot County, Maine, United States, near Old Town. The population was 758 at the 2020 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 used as a game preserve and hunting and gathering ground is in South Aroostook, Aroostook County, by which it passes along its way northward.

The Penobscot are an Indigenous people in North America from the Northeastern Woodlands region. They are organized as a federally recognized tribe in Maine and as a First Nations band government in the Atlantic provinces and Quebec.