 During that time, Fort Sheridan was the headquarters for activities at 74 U.S. Army Reserve Centers located in northern Illinois, northwest Indiana, and the lower peninsula of Michigan.HQ Fourth US Army, was at "The Army's Biggest Little Post", Fort Sheridan.The Fort was founded in 1887, named for Gen. Philip H. Sheridan, Civil War Union cavalry leader and commanding general of the Army, 1883–1888; It is located on 695 acres on the shore of Lake Michigan, 29 miles north of Chicago loop.