Fort Collins was founded as a military outpost of the United States Army in 1864. It succeeded a previous encampment, known as Camp Collins, on the Cache La Poudre River, near what is known today as Laporte. Camp Collins was erected during the Indian wars of the mid-1860s to protect the Overland mail route that had been recently relocated through the region. Travelers crossing the county on the Overland Trail would camp there, but a flood destroyed the camp in June 1864. Afterward, the commander of the fort wrote to the commandant of Fort Laramie in southeast Wyoming, Colonel William O. Collins, suggesting that a site several miles farther down the river would make a good location for the fort. The post was manned originally by two companies of the 11th Ohio Volunteer Cavalry and never had walls.
Settlers began arriving in the vicinity of the fort nearly immediately. The fort was decommissioned in 1867. The original fort site is now adjacent to the present historic "Old Town" portion of the city. The first school and church opened in 1866, and the town was platted in 1867. The civilian population of Fort Collins, led by local businessman Joseph Mason, led an effort to relocate the county seat to Fort Collins from LaPorte, and they were successful in 1868.
The city's first population boom came in 1872, with the establishment of an agricultural colony. Hundreds of settlers arrived, developing lots just south of the original Old Town. Tension between new settlers and earlier inhabitants led to political divisions in the new town, which was incorporated in 1873. Although the Colorado Agricultural College was founded in 1870, the first classes were held in 1879.
The 1880s saw the construction of a number of elegant homes and commercial buildings and the growth of a distinctive identity for Fort Collins. Stone quarrying, sugar-beet farming, and the slaughter of sheep were among the area's earliest industries. Beet tops, an industry supported by the college and its associated agricultural experiment station, proved to be an excellent and abundant food for local sheep, and by the early 1900s the area was being referred to as the "Lamb feeding capital of the world." In 1901 the Great Western sugar processing plant was built in the neighboring city of Loveland.
Although the city was affected by the Great Depression and simultaneous drought, it nevertheless experienced slow and steady growth throughout the early part of the twentieth century. During the decade following World War II, the population doubled and an era of economic prosperity occurred. Old buildings were razed to make way for new, modern structures. Along with revitalization came many changes, including the closing of the Great Western sugar factory in 1955, and a new city charter, adopting a council-manager form of government in 1954. Similarly, Colorado State University's enrollment doubled during the 1960s, making it the city's primary economic force by the end of the century.