Judy Cates was born on April 22, 1952 and was raised in Belleville, Illinois. She attended Cornell University, receiving a B.A. in Government in 1973. She went on to receive her juris doctorate in 1977 from the Washington University School of Law - St. Louis. Before joining the Appellate Court, Judy Cates first practiced law as an Assistant State's Attorney for St. Clair County, Illinois. After leaving the State's Attorney's office, she entered private practice, concentrating in complex litigation cases, such as personal injury, class actions, mass actions, sexual harassment and corporate disputes. Justice Cates was engaged in the private practice of law for 30 years prior to being elected to the 5th District Appellate Court in 2012. She was admitted to practice law in Illinois, Missouri and Florida, and maintains her licenses in these states. She remains a member of the Illinois State Bar Association, Missouri Bar Association, and Florida Bar Association, as well as her local Bar Association. She was also admitted to practice in many federal courts across the country and enjoyed a nationwide reputation. Justice Cates was the first woman to serve as President of the Illinois Trial Lawyers Association, was named one of the Top 50 Women lawyers in the State of Illinois and recognized by her peers as a SuperLawyer with a Martindale-Hubbell rating of AV-Preeminent.

Prior to being elected to the Appellate Court, Justice Cates taught Complex Litigation at the Washington University School of Law and Trial Advocacy at St. Louis University School of Law. Once elected, Justice Cates has served, and continues to serve, as a Moot Court judge for the S.I.U. School of Law and Washington University School of Law. Justice Cates also served as the representative of the 5th District at the State of Illinois Judicial Conferences, teaching "Updates in Criminal Law" from 2012 to 2018. Justice Cates is a member of the Illinois Judges Association, the Illinois Bar Association (and member of the Bench & Bar Committee), and currently serves on a Supreme Court sub-committee developing a program for people to access the appellate court with the assistance of free legal aid. Justice Cates volunteers for that position. She is married to Darrell Cates, and they have three children - Dave, Lauren, and Robby.