group of over 1,500 islands in the St. Lawrence River at the outlet of Lake Ontario, some forming part of N.Y. state & others forming part of Ontario, Canada
See Thousand Islands in American Heritage Dictionary 4
A group of more than 1,800 islands of northern New York and southeast Ontario, Canada, in the St. Lawrence River at the outlet of Lake Ontario. The islands, some of which are privately owned, are a popular resort area.