Nitpick: Ceres is in the Asteroid Belt and was discovered in 1801. Its discovery was not unlike that of Pluto, and it was considered to be a planet until after several other asteroids were discovered.

Pluto's discovery and eventual recategorization was pretty much the same situation, except that every new Kuiper Belt Object wasn't being counted as another new planet. When Eris was discovered, which is larger than Pluto, it forced the IAU's hand in creating an actual definition for "planet".