705 ILCS 205/10
No coroner, sheriff or deputy sheriff shall be permitted to practice as an attorney or counselor at law in the county in which he is commissioned or appointed, nor shall any clerk or deputy clerk of a court be permitted to practice as an attorney or counselor at law in the court in which he is such clerk or deputy clerk, and no person shall be permitted or suffered to enter his name on the roll or record, to be kept as aforesaid, by the clerk of the Supreme Court, or do any official act appertaining to the office of an attorney or counselor at law, until he has taken the oath hereinbefore required; and the person administering such oath shall certify the same on the license, which certificate shall be a sufficient voucher to the clerk of the Supreme Court to enter or insert, or permit to be entered or inserted, on the roll of attorneys or counselors at law, the name of the person of whom such certificate is made.
705 ILCS 205/10