The Marias Massacre was a massacre of Piegan Blackfeet Native peoples which was committed by the United States Army as part of the Indian Wars. The massacre occurred on January 23, 1870, in Montana Territory. Approximately 200 Native people were killed, most of whom were women, children, and older men.

The Piegan are an Algonquian-speaking people from the North American Great Plains. They are the largest of three Blackfoot-speaking groups that make up the Blackfoot Confederacy; the Siksika and Kainai are the others. The Piegan dominated much of the northern Great Plains during the nineteenth century.