Founded in the 1870s, the present-day site of Clyde Park was originally founded as Sunnyside by Texas cattlemen who were attracted to the area for grazing their herds. The post office in Sunnyside was established in 1887. In 1887, a post office called Clyde Park was established at the historic Harvey and Tregloan Ranch, where John Harvey owned a Clydesdale horse which he had imported from England in the late 1890s.
In 1901, the Clyde Park post office was merged with Sunnyside, and the town was renamed Clyde Park. However, the reason is unclear. Another source suggests that the town was called Clyde Park in honor of Clyde Durand, a local rancher; or for Harvey's Clydesdale horse.
In 1909 the Northern Pacific Railway established a branch line to the town, and in 1912 it incorporated as Clyde Park. That year it was reported to have a bank, a newspaper, a creamery, and an elevator. A major fire burned much of the town in 1919.
The town is also home to the Old Settler's Days, an annual celebration of pioneer history. It includes an art show, parade, and more.
(Information gathered from Wikipedia - https://en.wikipedia.org/wiki/Clyde_Park,_Montana)