Allen was born in approximately 1877 and was a resident of Sac City, Iowa. He was the son of William Allen (born c. 1816 in Virginia) and Sarah Allen (born c. 1847 in Wisconsin). At the time of the 1880 United States Census and the 1885 Iowa Census, the family was living at Sac City. As a third-year student, Allen was the coach of the varsity reserves football team. He graduated from Michigan with a Bachelor of Laws degree as part of the Class of 1900.