When you seek a divorce in Illinois, you must give a reason to the court. According to the Illinois Courts, the only reason allowed in this state is irreconcilable differences. 

You cannot declare grounds that the other person did something to make you want to end the marriage because Illinois is a no-fault divorce state. 

Definition 

Irreconcilable differences mean that you do not want to remain married to your spouse because you no longer get along. It is a simple matter of just not wanting to be in the relationship so you ask the court to legally end the marital agreement. 

Separation requirement 

While every couple must file on the ground of irreconcilable differences, there is also a separation requirement to file. You and your spouse must live apart for at least six months. If you cannot meet this requirement, then you will need to show the judge that you and your spouse have tried to repair the marriage but decided that this was not possible and the only solution is to divorce. You may also show proof that the situation is detrimental to the well being of your family if you were to remain in the marriage. 

Other proof 

Besides showing you meet the separation requirement, you do not have to provide any further proof that you and your spouse have irreconcilable differences. This is because the court will not assign fault to either of you for the breakdown of the marriage. This is in contrast to other states that do have fault grounds and do require proof to accept the grounds.