1864    Montana is organized as a United States territory.

1867    Atlantic Cable Quartz Lode gold mine located in Montana.

1870    In Montana, U.S. cavalrymen kill 173 Native Americans, mostly women and children, in the Marias Massacre.

1873    Indian Wars: whilst protecting a railroad survey party in Montana, the United States 7th Cavalry, under Lieutenant Colonel George Armstrong Custer clashes for the first time with the Sioux near the Tongue River; only one man on each side is killed.

1887    In a snowstorm at Fort Keogh, Montana, the world's largest snowflakes are reported, {{convert|15|in|cm}} wide and {{convert|8|in|cm}} thick.

1889    President Grover Cleveland signs a bill admitting North Dakota, South Dakota, Montana and Washington as U.S. states.

1889    Montana is admitted as the 41st U.S. state.

1910    An act of the U.S. Congress establishes Glacier National Park in Montana.

1917    Jeannette Rankin of Montana becomes the first female member of the United States House of Representatives.

1943    The Smith Mine #3 in Bearcreek, Montana, explodes, killing 74 men.

1959    Quake Lake: Quake Lake is formed by the magnitude 7.5 1959 Yellowstone earthquake near Hebgen Lake in Montana.

1996    Suspected "Unabomber" Theodore Kaczynski is arrested at his cabin in Montana, United States.