Eastern Montana is a loosely defined region of Montana. Some definitions are more or less inclusive than others, ranging from the most inclusive, which would include the entire part of the state east of the Continental Divide, to the least inclusive, which places the beginning of "eastern" Montana roughly at or even east of Billings, Montana. The areas of Montana lying just east of the Continental Divide are often called Central Montana. A widely accepted definition of Eastern Montana is that it encompasses the eastern third of the state.

The Crow, whose autonym is Apsáalooke, also spelled Absaroka, are Native Americans living primarily in southern Montana. Today, the Crow people have a federally recognized tribe, the Crow Tribe of Montana, with an Indian reservation, the Crow Indian Reservation, located in the south-central part of the state.