Gardiner is a census-designated place (CDP) in Park County, Montana, United States, along the 45th parallel. The population was 875 at the 2010 census.
Gardiner was officially founded in 1880, but the area has served as a main entrance to Yellowstone National Park since its creation in 1872. Parks' Fly Shop, one of the oldest fly shops and guiding operations in the Yellowstone area, was started by Merton Parks in 1953. Yellowstone National Park Heritage and Research Center, which opened May 18, 2005, is located in Gardiner and houses National Park Service archives, Yellowstone museum collections and reference libraries.
The name Gardiner derives from Johnson Gardner, a fur trapper who operated in the area in 1830-31. He named the lush headwaters valley of today's Gardner River Gardner's Hole. Originally, named Gardner's Fork, the river took on Gardner's name although prospectors and explorers who visited the area later in the century were unaware of the trapper Johnson Gardner. In 1870, when the Washburn-Langford-Doane Expedition passed through the area they began calling the river Gardiner—a phonetic error. Hiram M. Chittenden (1895) and Nathaniel P. Langford (1905) confirmed this spelling in their accounts of the expedition.
When the Hayden Geological Survey of 1871 passed through the Gardiner area, they encountered two men, named J.C. McCartney and H. R. Horr, who had laid claim to 320 acres (1.3 km2) and established a ranch and bath house on the Mammoth terraces near Liberty Cap. These entrepreneurs eventually established a primitive hotel at Mammoth and were not evicted from the area until many years after the park was established. McCartney also went by the name Jim Gardiner and received messages, consignments and such destined for guests of his hotel addressed to: Jim on the Gardiner.