1. On December 20, 1864, a battle known as the Battle of Reed's Creek took place in Bannack, Montana between Native Americans and a group of soldiers led by Captain James L. Fisk. The battle resulted in the death of several Native Americans and soldiers, and is considered one of the last major conflicts in the Montana Indian Wars.

2. In 1876, the Territorial Legislature of Montana officially recognized the University of Montana as a public institution, making it the oldest university in the state. December 20 is recognized as the university's Founders Day in honor of the occasion.

3. On December 20, 1944, the United States Army Air Forces' 2nd Air Division conducted a bombing raid over Leipzig, Germany, which was heavily defended by anti-aircraft artillery. Despite the intense opposition, the mission achieved its objectives and played a crucial role in the Allied victory in World War II.

4. In 2002, a snowstorm known as the "Christmas Eve Blizzard" hit Montana, dumping over 20 inches of snow in some areas and causing widespread damage and power outages. The storm began on December 20 and continued through Christmas Day.

5. December 20, 2020 marked the centennial anniversary of the Butte-Anaconda strike, one of the largest and most significant strikes in Montana's history. The strike involved copper miners and other workers demanding higher wages, safer working conditions, and recognition of their union. The strike lasted for over five months and ended with the creation of a new union and increased bargaining power for workers.