15 ILCS 405/8
In order to simplify methods for accounting and the issuance of warrants, the comptroller may establish a uniform system of code numbers for each appropriation and standard object and purpose therein made by the General Assembly, for each fund in the State treasury, for each fund held by the State Treasurer outside of the State treasury, and without limiting the foregoing, for each budgetary and proprietary account. The prescribed code numbers may identify the agency, division or institution, the purpose of the appropriation, the program, character of expenditure, appropriation act or other expenditure authorization, and the object of expenditure as defined in "An Act in relation to state finance", approved June 10, 1919, as now or hereafter amended. "Character of expenditure" as used in this Section means classification as capital, operating expenses, grants, loans, refunds, debt services, or other similar classification. The Comptroller may also include as part of the uniform system of code numbers, code numbers in such further detail as the comptroller finds necessary or desirable in the exercise of his powers and duties. A list showing the code numbers established pursuant to this Section shall be filed with the Secretary of State as a public record. Such list may be revised from time to time as necessary by filing a new list with the Secretary of State.
After such a list has been so filed, the code numbers set out therein shall be used on all vouchers submitted to the comptroller and on such other documents and forms as the comptroller may prescribe.
Copies of any such list filed with the Secretary of State shall be prepared by the comptroller for distribution to each State agency.
15 ILCS 405/8