Cool morning

Mt. Forest Island isn't much of a mountain and these days you would be hard pressed to call it an island. It does, at least, have trees.  

 The land here previously resided where Lake Michigan is now.  When the Wisconsinan glacier melted this was part of an earthen dam that created an area of still water behind it.  This silted in forming much of the land along the lakeshore.  When Chicago was still the Chicago Portage, much of the area was a swamp.  (The wet kind; the political kind came later.)  Shallow standing water was not uncommon at different times in the year and early topo maps showed multiple ponds and sloughs throughout the area.  As such, it wasn't much of a stretch to call the dry areas islands. Mt. Forest was the largest in the area.  To the east is Stoney Island (extending between Worth and Alsip IL) and still further east is Blue Island and the eponymous town which sits atop it.  

Canals, drainage ditches, sewer systems, and pumps have drained much of the land and rendered the island names meaningless...MOST of the time!