Gregory is a city in Gregory County, South Dakota, United States. The population was 1,295 at the 2010 census.
As the United States was racing into the 20th century, Gregory County was part of the "Last Frontier" opened to settlers. The Arikara and Ree Indians had long since vanished. The Sioux, who roamed the area since the mid-19th century, had been relegated to the Rosebud, Pine Ridge, Cheyenne, Standing Rock and Lower Brule reservations, and an ambitious congressman had persuaded President Theodore Roosevelt to open the territory for settlement.
The presidential proclamation was made public on May 15, 1904 which opened western Gregory County for settlement. Registration was held throughout the month of July, and on the 28th of that month, 2600 lucky land seekers received their 160-acre (0.65 km2) tracts.