About Glencross, South Dakota
Glencross is an unincorporated community in Dewey County in the U.S. state of South Dakota. Although it is unincorporated, it has a post office and has been assigned the ZIP code of 57630. It is located within the Cheyenne River Indian Reservation. Glencross was founded in 1919 by Conrad Mattern, who owned and operated the first store in the town. The town's name reportedly comes from its location where two valleys, or glens, intersect.