From Wikipedia:
Origin of name
Idaho is the only state that was likely named as the result of a hoax (the so called "Idahoax"). In the early 1860s, when the United States Congress was considering organizing a new territory in the Rocky Mountains, eccentric lobbyist George M. Willing suggested the name "Idaho," which he claimed was derived from a Shoshone language term meaning "the sun comes from the mountains" or "gem of the mountains." Willing later claimed that he had made up the name himself[3][4]. Congress ultimately decided to name the area Colorado Territory when it was created in February 1861.