Cascade County was formed in 1887 from Chouteau, Meagher, and Lewis and Clark Counties while Montana was still a territory.
At the time of the Lewis and Clark Expedition, Cascade County was the territory of the Blackfeet. The county was named for the falls on the Missouri River.
The United States Army at one time had Fort Shaw as an outpost in the northwest part of the county. Only a small settlement is left by that name, a Census-Designated Place.
According to the United States Census Bureau, the county has a total area of 2,711 square miles, of which 2,698 square miles is land and 13 square miles (0.5%) is water. The Missouri River and the Sun River flow through the county, and meet at the city of Great Falls. A portion of the Adel Mountains Volcanic Field is in the southwest corner of the county. The Rocky Mountains are in the western part of the county with the Little Belt and Highwood Mountains in the southeast.
Malmstrom Air Force Base is a driving force in the regional economy. In 2009, Benefis, Great Falls Clinic, National Electronics Warranty and Walmart were the largest private employers.