Calais (pronounced "CAL-us") Maine, is located "Downeast" in Washington County.It is in the heart of the St. Croix River Valley. With its 4,000 residents it sits across the river from its Canadian neighbor St. Stephen, New Brunswick. Calais is the fifth busiest port of entry to the United States on the Canadian border. excerpt from the Calais Maine Chamber of Commerce.It is in the heart of the St. Croix River Valley. With its 4,000 residents it sits across the river from its Canadian neighbor St. Stephen, New Brunswick. Calais is the fifth busiest port of entry to the United States on the Canadian border. excerpt from the Calais Maine Chamber of Commerce.