In the mid 1920's, the American Bison Society disappeared at the same time as the U.S. Post Office issued a stamp honouring the species. At its peak, pre-1800, the buffalo herd on the Great Plains numbered 60 million. However, by 1900, their number was reduced to 300.
Alfred Jacob Miller's painting courtesy https://en.wikipedia.org/wiki/American_bison#Range_and_population.
In 1894, Yellowstone National Park was the first to offer a sanctuary for the buffalo. A private citizen from Colorado also offered a reserve for the animals. No longer on the brink of extinction, as of 2000, the buffalo population had reached 360,000. Whereas before the buffalo population covered the map of North America, now they dot the map.
Note: For more information on the near extinction of the buffalo, visit http://alinefromlinda.blogspot.ca/2014/09/the-buffalo-storm.html.