This Tiny Island Is Split Between Michigan and Ohio
The island's history goes back to Native Americans who gathered seagull eggs there. With the coming of Europeans, the British established a fort on the island to defend the mouth of the Maumee River at Toledo. After the island came under control of the United States, a lighthouse was established and was in operation until 1904. This photo shows was the lighthouse looked like before its destruction.
The island's dual-state status came as a result of the infamous Toledo War which gave the Toledo Strip (far northern Ohio) from Michigan Territory to Ohio while Michigan received its Upper Peninsula. This is also the decision that took the lost villages of Vistula and Port Lawrence from Michigan. Today they are incorporated into Toledo.
Tiny Turtle Island was largely forgotten until a 1973 US Supreme Court decision in Michigan v Ohio finally settled the states' border right in the middle of the island:
The boundary line between the States of Ohio and
Michigan in Lake Erie follows a line drawn from the point
in Maumee Bay where the north cape of that bay was
located in 1836 on a course having a bearing North 450
East measured from a true meridian, passing over the
center of the existing circular concrete seawall on Turtle
Island and continuing on the same course through the lake to the point where it intersects the boundary line
between the United States and Canada.
The island is remote, a 3-4 mile paddle from the nearest shorelines in Michigan or Ohio, and while privately owned and not accessible to the public, a Wikipedia article on the island notes, that restricting access is nearly unenforceable.
This site contains a full history of the small island and take a virtual canoe trip to Turtle Island and check out some of the ruins: