Park County was created by the territorial legislature February 23, 1887. Prior to the 1880s, the region was Crow territory. The first record of white men in the region was Lewis and Clark.

Trapping, mining, ranching, and tourism opened the region to settlement in the mid- and late 1800s. By 1880, the population for the county was only about 200. This led to the creation Yellowstone National Park by Congress in 1872, the country’s first national park.

In 1881, the Northern Pacific Railroad, building a line westward, entered the state of Montana. Livingston was reached on November 22, 1882 where a settlement of 500 people had sprung up. That same year it opened its central repair facility and established Livingston as a major transportation hub in the region. In 1883, the National Park Branch of the NP Railroad was completed and the east west sections of the railroad joined together near Garrison, opening up the entire country to rail.

Following these events, the local area had a period of rapid growth. By 1890, the county had a population of 6,900. Steady growth since then has brought the county to where it is today.