Allen is a census-designated place on the Pine Ridge Indian Reservation in Bennett County, South Dakota, United States, that was named for the Allen Township, which it encompasses. As of the 2020 census, the CDP had a population of 460. It is one of two places which are closest to the North American continental pole of inaccessibility.

The Pine Ridge Indian Reservation, also called Pine Ridge Agency, is an Oglala Lakota Indian reservation located in the U.S. state of South Dakota, with a small portion of it extending into Nebraska. Originally included within the territory of the Great Sioux Reservation, Pine Ridge was created by the Act of March 2, 1889, 25 Stat. 888. in the southwest corner of South Dakota on the Nebraska border. It consists of 3,468.85 sq mi (8,984 km2) of land area and is one of the largest reservations in the United States.