 888).Despite its reservation status, most of the county was opened for settlement by the Act of May 27, 1910, where the US Congress "authorized and directed the Secretary of Interior to sell and dispose of all that portion of the Pine Ridge Indian Reservation, in the State of South Dakota, lying and being in Bennett County".Open settlement was ended by a Secretarial Order of June 10, 1936, which restored "to tribal ownership of all lands which are now, or may hereafter be, classified as undisposed-of surplus opened lands of the Pine Ridge Reservation..."

The county was created in 1909, with land partitioned from Fall River County.