Castor is a village in Bienville Parish in north Louisiana, United States. The population was 209 at the 2000 census but increased 23% to 258 in 2010. The median age is 32.2 years. The village was established in 1900. The name "Castor" refers to the genus Castoridae or beaver, a Latin term, contrary to an oral tradition of the word being Native American in origin.
Castor's ZIP code is 71016, and the local landline AT&T telephone numbers start with 544, with wireless number prefixes varying according to service provider. A number of surrounding smaller villages, both incorporated and not, including Roy, utilize the ZIP code of Castor.