Interesting that Google Maps shows the name of the state part at the southern tip of Plum Island as Plum Island State Park when the actual name of the park is Sandy Point State Reservation according to Mass. DCR, which runs the Massachusetts state park system. Also interesting that Wikipedia, of which I am usually a little skeptical, gets the name right.
As far as I can tell, Google Maps is the source of the mistake. That is, the other incorrect references seem to refer back to Google Maps. So, has somebody at Google renamed a Massachusetts state park base on what strings people search for rather than what the place is actually named? Fascinating.