Calais is a city in Washington County, Maine, United States. As of the 2020 census, it had a population of 3,079, making Calais the third least-populous city in Maine. The city has three Canada–US border crossings over the St. Croix River connecting to St. Stephen, New Brunswick, Canada.

Saint Croix Island, long known to locals as Dochet Island, is a small uninhabited island in Maine near the mouth of the Saint Croix River that forms part of the Canada–United States border separating Maine from New Brunswick. The island is in the heart of the traditional lands of the Passamaquoddy people who, according to oral tradition, used it to store food away from the dangers of mainland animals. The island was the site of an early attempt at French colonization by Pierre Dugua, Sieur de Mons in 1604. In 1984 it was designated by the United States Congress as Saint Croix Island International Historic Site. There is no public access to the island, but there is a visitor contact station on the U.S. mainland and a display on the Canadian mainland opposite the island.