It is located just east of the northern tip of Grosse Ile (Hennepin Point) and about 500 feet (152 m) west of the Canada–United States border.

The island is part of Grosse Ile Township in Wayne County, Michigan.

The shoal is about 3–8 feet (0.9–2.4 m) beneath the surface and runs all the way to Grassy Island.

[4] The area, including Mamajuda Island, has since become part of the Detroit River International Wildlife Refuge.

[6] However, the loose composition of the island was subject to slow erosion that eventually washed away the lighthouse in 1950.