Illinois constitution
Article VI
Section 8

Each Circuit Court shall have such number of Associate
Judges as provided by law. Associate Judges shall be
appointed by the Circuit Judges in each circuit as the
Supreme Court shall provide by rule. In the First Judicial
District, unless otherwise provided by law, at least
one-fourth of the Associate Judges shall be appointed from,
and reside, outside Chicago. The Supreme Court shall provide
by rule for matters to be assigned to Associate Judges.