1. Montana became an official territory of the United States on April 23, 1864. President Abraham Lincoln signed the legislation that established the territory, which was carved out of existing territories including Idaho and Dakota.

2. On April 23, 1889, the first official Earth Day was celebrated in Montana. It was organized by a group of environmental activists who were concerned about the damage being done to the state's natural resources, particularly its forests and rivers.

3. April 23, 1914, was the day of the famous shootout between law enforcement and the notorious outlaw Henry Plummer. Plummer and his gang had been terrorizing the Montana Territory for years, but were finally brought to justice in a dramatic showdown in the town of Bannack.

4. In 1923, on April 23, the Montana State Capitol building was completed. It remains one of the most notable landmarks in the state, featuring a distinctive copper dome that is visible for miles around.

5. On April 23, 1985, the FBI arrested Theodore Kaczynski in his remote cabin near Lincoln, Montana. Kaczynski, who became known as the Unabomber, was responsible for a string of mail bombs that killed three people and injured many others over a period of 17 years. His capture was a major moment in the history of the state and the nation.