1. On May 21, 1881, the infamous outlaw Henry Plummer was hanged in Virginia City, Montana. Plummer was known for leading a gang of road agents who terrorized the mining camps of the area.

2. May 21, 1894 marks the founding of the town of Billings, Montana. Named after Northern Pacific Railway President Frederick H. Billings, the town quickly became a major hub for trade and transportation in the region.

3. In 1930, the historic Mercantile Building was completed in downtown Missoula on May 21st. The building, which remains one of the city's most recognizable landmarks, originally housed a department store and later became the headquarters of a local bank.

4. May 21, 1896 marks the birth of famous Montana artist and conservationist Charlie Russell. Known for his vivid depictions of the American West, Russell's paintings and sculptures continue to be celebrated today.

5. On May 21, 1996, Montana made national headlines when "Unabomber" Theodore Kaczynski was arrested at his remote cabin near Lincoln, Montana. Kaczynski, who had been sending mail bombs for nearly 20 years, was eventually sentenced to life in prison without parole.