Click on a picture for a larger display or Slideshow button (right) for automatic display. September 2018. The 1000 Islands region is made up of more than 1800 islands straddling the Canadian and USA border along the St Lawrence river. Many of the islands are privately owned and have houses of varying sizes built on them, and yet more along the seaway. Some islands feature huge houses and castles, Boldt Castle on Heart Island being the most famous.