What is often referred to as a “marriage annulment” in the Church is a declaration by a Church tribunal (a Catholic Church court) that a marriage thought to be valid according to Church law actually fell short of at least one of the essential elements required for a binding union.
In the Archdiocese of Chicago, annulments are handled by an agency called the Metropolitan Tribunal. Their web site provides a video explanation of their work and a list of frequently asked questions (in English and Spanish).
You may also find it helpful to consult the U.S. Conference of Catholic Bishops Annulments page.
If you’re looking for support during an annulment process, please contact Deacon Chris Murphy, Pastoral Associate at 847.864.1185 x242.