Gen.George B. McClellan assumed command of Union forces in western Virginia in June1861. On June 27, he moved his divisions from Clarksburg south against Lt. Col. John Pegram's Confederates, reaching the vicinity of Rich Mountain on July 9. Meanwhile, Brig. Gen. Thomas A. Morris's Union brigade marched from Philippi to confront Brig. Gen. Robert S. Garnett's command at Laurel Hill. On July 11, Brig. Gen. William S. Rosecrans led a reinforced brigade by a mountain path to seize the Staunton-Parkersburg Turnpike in Pegram’s rear. A sharp two-hour fight ensued in which the Confederates were split in two. Half escaped to Beverly, but Pegram and the others surrendered on July 13. Hearing of Pegram’s defeat, Garnett abandoned Laurel Hill. The Federals pursued, and, during fighting at Corrick's Ford on July 13, Garnett was killed. On July 22, McClellan was ordered to Washington, and Rosecrans assumed command of Union forces in western Virginia. Union victory at Rich Mountain was instrumental in propelling McClellan to command of the Army of the Potomac.
Source
CWSAC Battle Summaries, National Park Service (http://www2.cr.nps.gov/abpp/battles/bycampgn.htm)
He served in western Virginia, seeing action at the Battle of RichMountain, as well as at Carnifax Ferry.
Governor Oliver P. Morton commissioned Willich as colonel of the 32nd Indiana (an all-German regiment), and he led it at the Battle of Shiloh in the spring of 1862.
Returning to the Federal army later that year, he was assigned to command of the 1st Brigade, 2nd Division, XX Corps and served with distinction during the Tullahoma Campaign.