Coined by French fur trappers in the late 1700s or early 1800s, La Grand Isle was a large island on the braided Platte River in central Nebraska. Traveling between Missouri and the Rocky Mountains, the island was a landmark along what would become the Great Platte River Road. Accounts estimated the island was 40-72 miles long.
It disappeared when the river was dammed to prevent seasonal flooding, but other large island such as Shoemaker Island Mormon Island remain. You can visit these modern Platte River islands by visiting the Crane Trust Nature & Visitor Center along Interstate 80.