Castor is an unincorporated community in the northwestern part of Filmore Township in Bollinger County, Missouri, United States.

The Castor River was in turn named for the Greek word kastor, meaning beaver.

[4] The name was given by the French who came to the Mine La Motte district.

The name was on account of the many beavers and their damns found along the river.

This Bollinger County, Missouri state location article is a stub.