When changing anyone’s name in Illinois you must proceed under statute 735 ILCS 5/21-101 which requires that the person whose name is being changed be an Illinois resident for at least 6 months.
You may change your name, your spouse’s name and your children’s name all together, if you so desire, under the same petition.
In changing a child’s name, though, the court must take special care.
“An order shall be entered as to a minor only if the court finds by clear and convincing evidence that the change is necessary to serve the best interest of the child. In determining the best interest of a minor child under this Section, the court shall consider all relevant factors, including:
(1) The wishes of the child’s parents and any person acting as a parent who has physical custody of the child.
(2) The wishes of the child and the reasons for those wishes. The court may interview the child in chambers to ascertain the child’s wishes with respect to the change of name. Counsel shall be present at the interview unless otherwise agreed upon by the parties. The court shall cause a court reporter to be present who shall make a complete record of the interview instantaneously to be part of the record in the case.
(3) The interaction and interrelationship of the child with his or her parents or persons acting as parents who have physical custody of the child, step-parents, siblings, step-siblings, or any other person who may significantly affect the child’s best interest.
(4) The child’s adjustment to his or her home, school, and community.” 735 ILCS 5/21-101
“The burden of proof in such cases is a high one, as the statute clearly states that a name-change order shall be entered as to a minor only if the court finds by clear and convincing evidence that the change is necessary to serve the best interest of the child.” In Re Marriage of Piegari, 2016 IL App (2d) 160594
Other court cases have held that “the consistent use of a single name is important to the child’s emotional development.” In Re Marriage of Presson 102 Ill. 2d 313.
You may even have “full custody” or absolute control of all aspects of your child’s life and the other parent may not even be in the child’s life yet you will still have to get the court’s permission and meet this very high standard to change the child’s name.
If you cannot change the child’s name officially and start referring to the child by another name, whether in school registration or even social media, the other parent can ask the court for an injunction to force you to use the child’s official name.
In my personal experience, most child name changes happen when two people have a child without being married. The mother will often give the child her maiden name and the father will later petition to change the child’s name when he tries to get parenting time. In this scenario, the court often doesn’t take such a formal analysis and encourages the parties to settle by hyphenating the last names. But, after a hearing, the father’s last name is typically chosen as the child’s last name.
In the case where the child knows his or her own last name, typically at 2 or 3 years old, the court will refrain from changing the child’s last name to match the father’s last name. So, act quickly.