Before any parent signs on the dotted line to their custody agreement, they should understand each and every provision of the document. Hastily signing an agreement thinking that one can “just go into court” and seek to have it changed at a later time is a mistake. In Illinois, unless the children are seriously endangered, a parent cannot ask the court to change custody for at least two years after the judgment is entered – and this includes seeking a change in the named primary residential parent.In Illinois, a court will employ a two-prong approach when deciding whether to change legal custody of a child when a custody judgment already exists. The first question the court will ask is whether there has been a change in circumstances of the child or the child’s custodian since the entry of the original custody judgment. If the court finds that no change of circumstances exists, then the analysis ends, and custody will not be modified.If the court finds that there is a change in circumstances, it will then employ a “best interest” test to decide whether a modification of custody is in the child’s best interest. Often times a Child Representative or Guardian Ad Litem will be appointed to represent the child in the court proceedings. The court may also choose to appoint a custody evaluator to prepare a report to aid the court in its determination of what is in the best interest of the children.Ultimately, the decision of whether custody will be modified lies within the discretion of the court. Section 602 of the Illinois Marriage and Dissolution of Marriage Act sets forth the best interest factors the court is required to consider in making its determination:The factors are the same as what the court would consider in an initial custody determination. However, courts generally favor stability in custody arrangements, and therefore, modifications to custody arrangements after the initial custody judgment is entered can be difficult to obtain.