Mills was born in Pleasanton, Kansas, near the Civil War Mine Creek Battlefield site, but moved to Colorado at the age of 14. He suffered from an unidentifiable illness which he later discovered to be an allergy to wheat. At age 15, he made his first ascent of the 14,255-foot Longs Peak. Over the course of his life, he made the trip 40 times by himself and nearly 300 additional times as a guide. He built his homestead near Longs Peak and the town of Estes Park, Colorado at the age of 15, completing it at 16.
In the winter of 1887 he moved to Butte, Montana. There he lived and worked intermittently until 1902, spending summers traveling or near his homestead in Estes Park. In 1889, he had a chance encounter with famed naturalist John Muir on a San Francisco beach, and from that point on Mills dedicated his life to conservation activism, lecturing, and writing.
In 1902, Mills returned to Colorado and purchased from his cousin the Longs Peak House near Estes Park. Mills hired and trained nature guides there, who guided many people up Longs Peak and the surrounding area. His methods of nature interpretation are still taught to students in the field of interpretation.
From 1902–1906, Mills also served as the Colorado State Snow Observer, a position that took him into the wild he so loved. His job was to measure the snow depths to predict spring and summer runoff. Following this position, he served as government lecturer on forestry from 1907–1909.
Mills contributed to the innovation of recreational industry. His speeches generally focused on the lives of trees, forestry issues, preservation of natural lands, and the lives of wild animals. Often in his speeches and written articles he encouraged people of all ages to get outside and into nature.
Mills also led the fight to preserve the area around Longs Peak and along the Continental Divide as a national park. He used his speeches, his writing, and photography to further his proposal even as he was met with stiff opposition. Aided by groups such as the American Civic Association, the General Federation of Women's Clubs, and other like-minded civic associations, Mills succeeded and Congress established Rocky Mountain National Park in 1915. He was called the "Father of Rocky Mountain National Park" by the Denver Post.
Mills continued to lecture and write books until his death at age 52 in 1922. He died from blood poisoning from an infected tooth.
Family and Relations
Enos A. Mills was born to Enos Mills, Sr., and Ann Lamb Mills. He had ten brothers and sisters, who are listed in order of birth: Augustus, Elkhanah F., Mary E., Naomi Victoria, Ruth, Sarah A., Ellen, Sabina Isabelle (Belle), Horace G., Enoch Joe. 
He married Esther Burnell on August 12, 1918. On April 27, 1919, Enda Mills was born. She was their only child.
- The Story of Estes Park and Guide Book (1905)
- Wild Life on the Rockies (1909)
- The Spell of the Rockies (1911)
- In Beaver World (1913)
- The Rocky Mountain Wonderland (1915)
- The Story of Scotch (1916)
- Your National Parks (1917)
- The Grizzly, Our Greatest Wild Animal (1919)
- The Adventures of a Nature Guide (1920)
- Waiting in the Wilderness (1921)
- Wild Animal Homesteads (1922)
Watched By Wild Animals (1923)
- The Rocky Mountain National Park (1924)
- Bird Memories of the Rockies
- Wild, Peter; Skov, Arny (illus.) (1979). Enos Mills. Boise, Idaho: Boise State University "Western Writers Series" (#36). pp. 47. ISBN 978-0884300601 OCLC 6006498
- Brachfeld, Aaron (09/03/2015). "Progressive economics - the Pure Profit of Enos Mills". the Meadowlark Herald (September). the Meadowlark Herald. Retrieved 09/03/2015. Check date values in:
- "Enos A. Mills Lineage". www.enosmills.com. Retrieved 2015-11-02.
- Rocky Mountain National Park Dayhiker's Guide, Jerome Malitz, Big Earth Publishing, 2005.
- Wild, Peter (July 29, 1977). "The Father of Rocky Mountain Park: Enos Abijah Mills". High Country News. Launder, WY: 1, 6–7.
- Wild, Peter (1979). "Enos Mills: Propagandist of the Rocky Mountains". Pioneer Conservations of Western America. Missoula, MT: Mountain Publishing. pp. 71–79.
- "Enos Mills of the Rockies" by Esther Burnell Mills and Hildegarde Hawthorne. 1934, Houghton Mifflin
- Biography of Enos Mills, National Park Service
- Short radio episode "Universal Kinship" from The Adventures of a Nature Guide, 1920, by Enos A. Mills, California Legacy Project.
- Works by Enos Mills at Project Gutenberg
- Works by or about Enos Mills at Internet Archive
- Works by Enos Mills at LibriVox (public domain audiobooks)
- Enos Mills Cabin Website