Keystone is a town in the Black Hills region of Pennington County, South Dakota, United States.

Keystone was heavily damaged in the 1972 Black Hills flood.

[6] According to the United States Census Bureau, the town has a total area of 2.86 square miles (7.41 km2), all land.

[7] At the 2010 census there were 337 people, 153 households, and 81 families living in the town.

It now operates passenger trains pulled by preserved steam locomotives.

Another prominent local attraction is The National Presidential Wax Museum, which features wax sculptures of every president in U.S. history and several notable Sioux Chiefs, inventors, and international political figures.

Carrie Ingalls (sister of Little House on the Prairie author Laura Ingalls Wilder) spent a significant part of her adult life there, living with her husband David N. Swanzey and his children.

Both Carrie and Mary died in Keystone, but were buried in the family plot in De Smet.