John W. Turner was born on March 23, 1956 in Lincoln, Illinois. He received his B.A. degree from the University of Illinois in 1978, where he received Phi Beta Kappa distinction. He earned his J.D. degree from the DePaul University College of Law in 1981. Judge Turner served as the Logan County Public Defender from 1984 to 1987. In 1988, he was elected Logan County State's Attorney and he was re-elected in 1992.

In 1994 Judge Turner was elected to the Illinois House of Representatives and was a member of the House Judiciary Criminal Law Committee and spokesman of the House Judiciary Civil Law Committee.  He was appointed to the 4th District Appellate Court in June 2001 and elected to a full term on the court in 2002.

Judge Turner maintained a private practice of law in Lincoln, Illinois during the time periods that he served as Logan County Public Defender and as state representative. He has been a guest lecturer at Lincoln College and he is an Honorary Alumnus of that institution. He is a member of the Illinois State and Logan County Bar Associations and the Illinois Judges' Association.