It was actually named after Pluto, the Roman god of the underworld.When Pluto was first discovered by Clyde Tombaugh in 1930, he was given the honor of giving it a name. Although they were calling it Planet X informally, they needed something that matched the rest of the planets in the Solar System. The name Pluto was suggested by Venetia Burney, an 11-year old school girl in England. She was interested in ancient mythology, and thought that Hades, the Greek god of the underworld, made a good name. She suggested Pluto, to match the Roman god names given to the other planets.

More Info: en.wikipedia.org