The no-fault ground is when your marriage is irretrievably broken and there is no likelihood it can be preserved and you and your spouse have lived separate and apart for 2 years (or 6 months if a waiver of the 2 years is signed by both parties);

A full list of the fault grounds that are available for a divorce filed in Illinois are as follows: (Requires proof or the case can be dismissed)
(1) Impotence;

(2) Previously married and never divorced;

(3) Adultery;

(4) the respondent has willfully deserted or absented himself or herself from the petitioner for the space of one year, including any period during which litigation may have pended between the spouses for dissolution of marriage or legal separation;

( 5) Habitual drunkenness for at least two years;

(6) Drug addiction for at least two years

(7) Repeated and extreme physical or mental cruelty

(8) Felony conviction or imprisonment

(9) Infection with a sexually transmitted disease.