With the creation of the Colorado Territory, present Grand County was part of a larger Summit County that stretched from the Continental Divide to the Utah and Wyoming borders. In 1874 the territorial government formally established Grand County, choosing Hot Sulphur Springs as the county seat.
The creation of Routt and Moffat Counties established the current western boundary of Grand County in 1877. The Colorado Supreme Court established the current northern boundary in 1886, settling a dispute between Grand and Larimer Counties over land near the mining camp of Teller, in present-day Jackson County (the decision gave the land to Larimer County).
The town of Grand Lake was laid out in 1879, and in 1881 the county seat was moved there due to a brief mining boom. This led to a feud between two political factions, one supporting Grand Lake and the other supporting Hot Sulphur Springs. The feud culminated in a deadly shooting in Grand Lake in 1883, which left three county commissioners and the county clerk dead. The county seat was returned to Hot Sulphur Springs in 1888, ending much of the bitterness.
White occupation of Middle Park expanded after the Utes had been moved to the western part of the state as per the Treaty of 1868. In the early 1880s Rudolph Kremmling built a general store on the ranch of a Dr. Harris in western Grand County; by 1885 the site had a post office called Kremmling. In 1888 ranchers John and Aaron Kinsey had part of their ranch platted as the town of Kinsey City. Kremmling moved his store to the Kinseys’ new town, and the current community of Kremmling developed around it, incorporating under that name in 1904.
Ranching and agriculture grew during and after the short mining boom in 1879, as the grass in Middle Park proved especially nutritious for cattle. One well-known ranch in the area was the Cozens Ranch. Built by Billy Cozens in 1874, the ranch also served as a stopping place for travelers coming across Berthoud Pass through the Fraser River valley. Cozens helped build the town of Fraser and served as its postmaster. Agriculture was limited by the climate and altitude of Grand County, but lettuce and hay became major cash crops for the region in the early twentieth century.
The first railroad arrived in Grand County in 1904, allowing for easier shipment of crops and livestock to market and easier access to Middle Park for tourists. The Denver, Northwest & Pacific Railroad, also known as the Moffat Road, reached Grand County by building a line over the Continental Divide at Rollins Pass. The railroad first reached the small town of Arrow, just beyond the pass, in 1904, and later that year it established the town of Granby, which connected train travelers to a stagecoach line that ran north to Grand Lake.
The Moffat line reached Kremmling in 1906, continuing north to Steamboat Springs. In 1928 the long-awaited Moffat Tunnel replaced the line over Rollins Pass. The tunnel allowed the railroad to go through the Continental Divide rather than over it.
The tunnel also included a pipeline to move mountain water to the Denver Metro area beginning in 1936. Later, in 1956, completion of the Colorado-Big Thompson Project further appropriated water from the Colorado headwaters for farming and urban development along the Front Range. Lake Granby, a large reservoir that is now Colorado’s third-largest body of water, was created in 1950 as part of the project and now serves as a popular tourist destination in the summer.