Gilfillan was born and raised in Mt. Gilead, OH, where his outdoorsman father (Merrill C. Gilfillan) worked as a naturalist for the state's Department of Natural Resources and helped inspire an early fascination with the natural world and its creatures. Gilfillan graduated in 1967 from the University of Michigan. He attended the University of Iowa Writer's Workshop for two years, studying with Ted Berrigan, Anselm Hollo, and George Starbuck, among others. He lived and worked in New York City for eight years and then moved to Colorado, which serves as a base for frequent expeditions to the Great Plains and other regions of America from which he reports in essays, poetry, and short stories.

Poetry

• Truck, Angel Hair Books, New York, 1970
• 9:15, Doones Press, Bowling Green, OH, 1970
• Skyliner, Blue Wind Press, Berkeley, 1974
• To Creature, Blue Wind Press, Berkeley, 1975
• Light Years: Selected Early Poems, Blue Wind Press, Berkeley, 1977
• River through Rivertown, The Figures, Great Barrington, MA, 1982
• Coppers and Blues, Plum Pit, Boulder, 1997
• On Heart River, Dayo, Denver, 1995
• Satin Street, Moyer Bell, Wakefield, RI, 1997
• The Seasons, Adventures in Poetry, New York | Boston, 2002
• Small Weathers, Qua Books, Jamestown, RI, 2004
• Undanceable, Flood Editions, Chicago, 2005
• Selected Poems, 1965-2000, Adventures in Poetry, New York | Boston 2005

Essays

• Magpie Rising: Sketches from the Great Plains, Pruett | Vintage | Bison, 1988 | 1990 | 2003
• Burnt House to Paw Paw: Appalachian Notes, Hard Press, West Stockbridge, MA, 1997
• Chokecherry Places: Essays from the High Plains, Johnson Books, Boulder, 1998
• Rivers & Birds, Johnson Books, Boulder, 2003

Fiction

• Sworn Before Cranes, Crown, New York, 1994
• Grasshopper Falls, Hanging Loose, Brooklyn, 2000