Castor is a village in Bienville Parish, Louisiana, United States. The population was 209 at the 2000 census. It was established in 1900. The name "Castor" refers to the genus Castoridae beaver.
Castor's Zip Code is 71016, and its telephone numbers start with 544. Both of these numbers are also used in the adjacent communities of Alberta, Roy, New Ramah, Ashland, and New Hope. Although not all these communities are recognized as townships, they are on Bienville Parish maps. People living adjacent to Castor, but not within the city limits, often file information as being "from Castor." The Castor Zip Code which rests against Jamestown, Kepler Lake, and Ashland is a more accurate representation of Castor's actual self-proclaimed population.
During the American Civil War, Castor supplied salt for the Confederate States of America. A salt works was operated west of Castor by Alfred P. King.