Littlejohn Island is an island and census-designated place (CDP) in the town of Yarmouth in Cumberland County, Maine, United States. The population of the CDP was 118 at the 2010 census.
It is part of the Portland–South Portland–Biddeford, Maine Metropolitan Statistical Area.
Littlejohn Island is located in Casco Bay at 43°45′41″N 70°7′36″W / 43.76139°N 70.12667°W. It is connected by a causeway to Cousins Island, which is connected by a bridge to the mainland in Yarmouth. According to the United States Census Bureau, the Littlejohn Island CDP has a total area of 0.73 square miles (1.9 km2), of which 0.35 square miles (0.9 km2) is the island and 0.39 square miles (1.0 km2), or 53.25%, is in the water surrounding the island.