Illinois circuit courts were established by the Constitution of 1818. The judges, who were also the justices of the Illinois Supreme Court, were appointed by the Illinois General Assembly and served during good behavior.¹ The period from 1818 to 1848 saw Supreme Court justices serving as circuit court judges from 1818 to 1824, 1827 to 1835, and 1841 to 1848.² Independent circuit court judges were appointed by the legislature from 1824 to 1827 and from 1835 to 1841.³ The Constitution of 1848 provided for the election of circuit judges to six-year terms.⁴ In 1934, two additional judges were elected for each circuit.⁵ The Judicial Amendment of 1962 created two classes of judge: circuit judges and associate judges. Both were elected to six-year terms.⁶ The terms of associate judges were shortened to four years by the Constitution of 1970, and it required that they be appointed by the circuit judges.⁷

Circuit court jurisdiction covered all criminal cases and all civil suits for more than $20.⁸ Circuit courts were empowered to hear appeals from justices of the peace as well as to naturalize citizens.⁹ In 1827, the courts gained the responsibility of seeing that prisoners in county jails were treated humanely.¹⁰ Since 1848, circuit courts have enjoyed almost an unlimited legal jurisdiction.¹¹ In 1872, the courts gained jurisdiction over election contests in counties.¹² This was extended in 1895 to cover contests for mayors and village presidents, in 1899 to cover contests for election to the state judiciary, and in 1965 to cover township officers.¹³ In 1921, circuit courts gained appellate jurisdiction over the decisions of the Illinois Commerce Commission.¹⁴ The Constitution of 1970 gave the courts unlimited rights to review the decisions of state administrative bodies.¹⁵

The office of clerk of the circuit court was created by the Constitution of 1818.¹⁶ Statutory duties were originally limited to selecting juries, but in 1827 these were expanded to include issuing process, entering all judgments into the court record, and keeping docket and fee books.¹⁷ In 1829, clerks began to keep a complete court record, and they were allowed to appoint deputies in 1831.¹⁸ From 1818 to 1848, clerks were appointed by the circuit judges, but the Constitution of 1848 made the office elective, with a four-year term.¹⁹ In 1849, circuit clerks assumed the duties of ex officio county recorders.²⁰ In 1865, clerks were required to keep index books to cases; in 1874, they were required to keep record books of the names of all parties to legal actions in the courts; and in 1933, they were required to file the monthly reports of the county defenders.²¹ In 1963, the duties of ex officio county recorder were transferred to the county clerk, and in 1970 the office of circuit clerk was deconstitutionalized.²²