William Eaegle was born on October 30, 1838, in Ohio to Isaac Eaegle and Jane Nightser. His father was a shoemaker and farmer who owned $2,000 of real estate and $500 of personal property in 1860. The family moved to Greenbush, Michigan, in the late 1840s, and Eaegle attended school there. He grew up near Willard N. Daggett, and the two eventually became close friends. Eaegle enlisted in the Union army on October 8, 1861, and mustered in as a private in Company B of the 3rd Michigan Cavalry on October 11. The regiment took part in the Battle of Corinth and spent much of the war stationed in Mississippi and Tennessee. He mustered out in San Antonio, Texas, on February 12, 1866.
Eaegle married Emmaline Daggett, his friend’s sister, in Greenbush on March 2, 1864, and their son Earnest was born around 1866. By 1870, he was working as a carpenter, and he owned $75 of real estate and $225 of personal property. The family moved to Cadillac, Michigan, sometime in the 1880s, and Eaegle continued to work as a carpenter. He remained in Cadillac for the rest of his life, passing away there on December 28, 1917.