Mary Amelia Ingalls was born near the town of Pepin, Wisconsin. She was the first child of Caroline and Charles Ingalls and older sister of writer Laura Ingalls Wilder, known for her Little House book series.

Keystone is a town in the Black Hills region of Pennington County, South Dakota, United States. The population was 240 at the 2020 census. It had its origins in 1883 as a mining town, and has since transformed itself into a resort town, serving the needs of the millions of visitors to the Mount Rushmore National Memorial, which is located just beyond the town limits. Keystone was heavily damaged in the 1972 Black Hills flood.