Long Island

The earliest records of Long Island date to 1643 where several native American tribes had settled there for some time, farming the land and fishing to sustain themselves. Each tribe lived peacefully in their own area and had good writing skills, which provides historians with written documentation of their life in these times.

With the arrival of the Europeans, everything changed. Henry Hudson landed at Coney Island in 1609, and Adriaen Brock in 1615 is generally recognised as the first person to declare Long Island was in fact an Island. 

This changed in 1985, when in the US Supreme Court it was legally declared to be part of New York State mainland, i.e. not an island, because it is not completely surrounded by water.

The misconception it was an island is perpetuated by the various maps and nomenclature from before and since this date which still calls it one, even though legally it is not.

Origin

The origins of what we now know as Long Island are not good. Western setters "paid" the local indigenous people four coats and $16.25, the problem being the locals didn't realise they were selling it off completely, and thought they were entering into a sharing partnership. Things turned sour in 1675 when war broke out, and the Dutch colonists drove the indigenous people off the island completely, leaving any that remained to die from smallpox which they had never encountered before, and hence had no natural resistance of.

The island was initially settled on after this war by the Dutch and the English. It next reatured during the American Revolution, when it was captured in its entirety by the British.

Looking on a map, it's pretty obvious there shouldn't be a problem calling it an island, but technically because it is connected by a short strip to the land it isn't completely surrounded by water. In any case, there doesn't seem much chance of it changing it's name to something other than Long Island any time soon...