Little Mark Island Monument, Stone navigation monument in Northern Casco Bay, Maine, United States.

The Little Mark Island Monument is a slender square stone pyramid, 50 feet (15 m) tall, on the treeless one-acre Little Mark Island in northern Casco Bay. Its base walls are 18 feet (5.5 m) long and taper to 4 feet 6 inches (1.37 m) at the top. Each face has vertical black stripes; a steel ladder on the south side and an open entrance on the west lead to an interior chamber rising to a concrete cap that holds the beacon equipment.

This structure was built in 1827 to help ships navigate along the Maine coast. A light signal was added in 1927 to further improve visibility for passing vessels.

The monument's black vertical stripes and pyramidal form echo the 1811 Cape Elizabeth structure it replicated; a 1923 counterpart stands on Stage Island off Biddeford. Its interior once held supplies for shipwreck survivors, and since 1927 a white light flashes 0.4 seconds every four seconds.

The island lies in northern Casco Bay, south of Haskell Island and west of the southern tip of Bailey Island, and has no visitor facilities, so bring food and water. The monument's west side has an open entrance; a steel ladder is mounted on the south side. The beacon's batteries are recharged by solar panels on a concrete pad outside.

The monument is a functional replica of an 1811 structure at Cape Elizabeth, where the Cape Elizabeth Lights now stand. A third similar tower was built on Stage Island off Biddeford in 1823 and still serves as an aid to navigation, making Maine's three examples a linked set.