Cyrus Dietz was born in Iroquois County, Illinois, March 17, 1876. He received his preliminary education at Grand Prairie Seminary and graduated from the College of Liberal Arts and Law School of Northwestern University in 1902. He began the practice of law at Chicago and came to Moline on January 1, 1904, where he continued to practice until elected Judge of the Supreme Court on November 6, 1928, to fill the vacancy caused by the resignation of Justice Thompson. He was a delegate to the Illinois Constitutional Convention of 1920 and served from January 1, 1925, until elected as Special Assistant Attorney General of Illinois, representing the State in the Lake Levels case then pending in the Supreme Court of the United States and in the Illinois Central charter fee litigation. Justice Dietz died September 13, 1929, at his home in Moline.