Born in Waterville, Minnesota, Dehn was the descendent of farmers who had emigrated from Germany. His family lived in rural poverty. His father, a hunter and trapper, was also an atheist and anarchist. His mother was a socialist and feminist, so Dehn was exposed to a wide range of radical thinking while growing up.[3] His mother encouraged Dehn’s artistic talent which was apparent at an early age. After graduating as valedictorian from Waterville High School, he went to the Minneapolis School of Art where he met a woman, Wanda Gág, who was to be Dehn’s close companion for the next five years. Both received scholarships to attend the Art Students League in New York. After graduation, Dehn was drafted to serve in World War I, but was imprisoned in Spartanburg, South Carolina after declaring himself a conscientious objector. Upon his release, he worked for several months as a volunteer painting teacher at an army rehabilitation hospital in Asheville, North Carolina. Dehn then returned to the Art Students League for another year of study and created his first lithograph, The Harvest.