1. On December 19, 1866, the United States Army launched a surprise attack on the Cheyenne tribe at Sand Creek in southeastern Montana, killing over 200 people, mostly women and children. This event, now known as the Sand Creek massacre, remains one of the darkest chapters in Montana's history.

2. In 1903, Montana's first public library was established in Butte on December 19. The library, which originally housed 6,000 books, was funded by a $50,000 donation from industrialist Andrew Carnegie.

3. On December 19, 1935, Montana's first state park was established when Makoshika State Park was created near Glendive. The park, which covers over 11,000 acres, is home to some of the most unique geological formations in the state.

4. In 1941, Montana Governor Sam Ford declared December 19 as "Montana Day" to mark the state's 78th anniversary of statehood. The holiday has since been celebrated annually with various events and activities across the state.

5. On December 19, 1980, an earthquake with a magnitude of 5.8 struck the town of West Yellowstone, causing significant damage to buildings and infrastructure. The earthquake was one of the largest ever recorded in Montana and served as a reminder of the state's active seismic activity.