1837 Great Plains smallpox epidemic

The 1837 Great Plains smallpox epidemic spanned 1836 through 1840 but reached its height after the spring of 1837, when an American Fur Company steamboat, the SS St. Peter, carried infected people and supplies up the Missouri River in the Midwestern United States. The disease spread rapidly to indigenous populations with no natural immunity, causing widespread illness and death across the Great Plains, especially in the Upper Missouri River watershed. More than 17,000 Indigenous people died along the Missouri River alone, with some bands becoming nearly extinct.

Having witnessed the effects of the epidemic on the Mandan tribe, fur trader Francis Chardon wrote: "the small-pox had never been known in the civilized world, as it had been among the poor Mandans and other Indians. Only twenty-seven Mandans were left to tell the tale." In 1839, the United States Commissioner of Indian Affairs reported on the casualties: "No attempt has been made to count the victims, nor is it possible to reckon them in any of these tribes with accuracy; it is believed that if [the number 17,200 for the upper Missouri River Indians] was doubled, the aggregate would not be too large for those who have fallen east of the Rocky Mountains."