Where is Grand Isle

Grand Isle is at the end of the road. Not any road- Louisiana Highway 1. You cross the Mississippi River on Baton Rouge, turn left, and keep driving for about three hours. When the road ends- you are in Grand Isle.

At least- for now. Barrier islands are continually moving as water and wind erode sand in some places, and deposit it in others. The image below shows the projected location of Grand Isle after a few decades of erosion and deposition.