As a general rule, the answer would be yes.

Even though a divorce or other family law matter is pending before the courts, neither party is barred from leaving the State of Illinois.  Basically, parents are free to travel, take vacations, attend business functions and training out of state without any repercussions.  There are restrictions when it comes to leaving the State with minor children.

If you plan on leaving the State with a minor child, AND a divorce or paternity case is pending, you should contact your attorney in advance.  There are provisions in the Marriage and Dissolution of Marriage Act which limits travel out of state with a minor child while a divorce is PENDING.  After a Judgement for Dissolution of Marriage is entered, there are probably notification requirements and limitations on how long you can be gone from the State.  Check your Judgment for expectations and limits of removing minor children from the State on a temporary basis.  Aside from the Illinois Marriage and Dissolution of Marriage Act, there are federal barriers and requirements before removing a child from the United States.

You should consult with your attorney BEFORE removing the minor child so the details can be worked out beforehand.