Wordorigins.org

One might think that that the state of Delaware is named for the Indian tribe. But in fact, the state, the river, and even the Indian tribe are named for the first English governor of Virginia, Thomas West, Lord Delaware (Baron De La Warr). The river was named by the first European to discover it, Captain Samuel Argall, in 1610. The colony and the Indians who lived in the area were named after the river.

The Delaware Indians’ native name for themselves is the Leni-Lenape.

(Sources: Illustrated Dictionary of Place Names; Webster’s Third New International Dictionary)