The majority of history pertaining to Grand Loop Road was taken from the below National Park Service article:
Yellowstone was declared the first National Park of the United States on March 1st, 1872. The first real highway to access Yellowstone National Park came in 1873 when a tolled facility was constructed from Bozeman, Montana via Yankee Jim Canyon to Mammoth Hot Springs. Numerous attempts were made to fund construction of roadway infrastructure during the early years of Yellowstone National Park but little success was found. Early Yellowstone National Park can be observed on the 1874 Map of the Military Department the Platte.
During the Auto Trail era numerous highways were plotted with Yellowstone National Park as their end point. During 1920 the National Park-to-Park Highway was created and plotted as a Auto Trail purposed with connecting the National Parks. During 1923 Yellowstone National Park publicist renamed the Belt Line Road as the "Grand Loop Road." The 1925 Rand McNally Autotrails Map of Idaho-Montana-Wyoming displays numerous Auto Trails ending at Yellowstone National Park or not having an implied through routes on the Grand Loop Road. From the West Entrance Road at West Yellowstone Montana the Utah-Idaho National Highway (3), Vigilante Trail (15), Geysers to Glaciers Highway (67) and a spur of the National Parks Highway (91) can be seen terminating at the Yellowstone National Park boundary. From the North Entrance Road in Gardiner, Montana the Yellowstone Trail (1), Yellowstone-Glacier "B" Line (14), Regina-Yellowstone Highway (17), a spur of the National Park-to-Park Highway (64) and a spur of the National Parks Highway (91) can be seen terminating at the Yellowstone National Park boundary. No Auto Trails are seen following the Northeast Entrance Road to Yellowstone National Park. From the East Entrance Road along the Shoshone River in Wyoming the Black and Yellow Trail (7), Buffalo Highway (8), National Parks Pike (9), Yellowstone Highway (13), Glacier to Gulf Highway (23), Shortcut West Highway (32), a spur of the National Park-to-Park Highway (64) and Wyoming Highway 26 can be seen terminating at the Yellowstone National Park Boundary. From the South Entrance Road along the Lewis River in Wyoming the Rocky Mountain Highway (22), Grant Highway (28) and Wyoming Highway 80 can be seen terminating at the Yellowstone National Park Boundary.
From the Grand Canyon of the Yellowstone southbound follows the Yellowstone River through Hayden Valley.
From Old Faithful Village the Grand Loop Road swings northward and crosses the Firehole River at Biscuit Basin. Northbound Grand Loop Road follows the Firehole River to the Midway Geyser Basin where Grand Prismatic Spring can be found.
Grand Loop Road northbound enters the Lower Geyser Basin where the Fountain Paint Pot Nature Trail can be found.
Northbound Grand Loop Road follows the Firehole River towards Madison Junction. Approaching the Gibbon River northbound Grand Loop Road intersects Firehole Canyon Drive.