70 ILCS 2605/5.5
At least 60 days prior to the beginning of the budget year, the heads of all departments of the district shall prepare and submit to the executive director detailed estimates of expenditure requirements with respect to the contributions each department or organizational unit is expected to make in achieving approved program objectives for the budget year, compared with the actual figures of the preceding year and the estimated figures for the current year. The expenditure estimates must be in detail and must be classified to set forth the data by funds, organization units, objects, character, and functions (activities) of expenditures in accordance with the classification of expenditure accounts adopted, or hereafter adopted, by the board of trustees. The detailed estimates of expenditure shall be accompanied by written statements of specific objectives to be achieved, the cost of achieving these objectives and supporting work units and unit cost data wherever applicable.
Within 15 days after the receipt of the department expenditure estimates, the executive director shall prepare and submit to the board of trustees a sufficient number of complete copies of the departmental estimates of expenditures together with the aggregate expenditure estimates in detail and his own estimate of receipts of the district for the ensuing fiscal year. The estimates of receipts must be in detail and must be classified to show the receipts by funds, and the several sources of receipts, including the proceeds to be derived from the sale of bonds, or other property, and must be in accordance with the classification of revenue accounts now or hereafter adopted by the board of trustees.
The board of trustees shall review the estimates both of anticipated receipts and of anticipated expenditures, adding to, altering, revising, increasing or decreasing the items of the estimates as it deems necessary in view of the needs and available and probable receipts of the district. The board of trustees shall then prepare a tentative budget setting forth the detailed estimates both of expenditures and receipts together with all supporting schedules, summary statements, drafts of the appropriation ordinance, tax levy ordinance and other ordinances necessary to give effect to the budget, in the form provided in Section 5.4 of this Act.
70 ILCS 2605/5.5