1. On May 17, 1862, the Homestead Act was signed into law by President Abraham Lincoln. This led to a significant increase in settlement and homesteading in Montana, as it allowed individuals to claim up to 160 acres of public land for free.

2. May 17, 1876, is known as the day of the Massacre of the Piegans. During this event, a group of US Army soldiers attacked a peaceful village of Native Americans, resulting in the deaths of over 170 men, women, and children.

3. On May 17, 1915, the first-ever transcontinental telephone line was completed in Montana. This allowed for direct communication between the East and West coasts of the United States.

4. In 1954, on May 17, the US Supreme Court issued its landmark decision in Brown v. Board of Education, which declared that segregation in public schools was unconstitutional. This ruling had significant implications for Montana schools, which were previously segregated.

5. May 17, 1979, saw the opening of the first phase of the Libby Dam on the Kootenai River in northwestern Montana. The dam, which was completed in 1983, provides hydroelectric power and flood control to the region.