35 ILCS 640/2-11
When electricity is used or consumed by a self-assessing purchaser subject to the tax imposed by this Law who did not pay the tax to a delivering supplier maintaining a place of business within this State and required or authorized to collect the tax, that self-assessing purchaser shall, on or before the 15th day of each month, make a return to the Department for the preceding calendar month, stating all of the following:
In making such return the self-assessing purchaser may use any reasonable method to derive reportable "purchase price" from the self-assessing purchaser's records.
If the average monthly tax liability of the self-assessing purchaser to the Department does not exceed $2,500, the Department may authorize the self-assessing purchaser's returns to be filed on a quarter-annual basis, with the return for January, February and March of a given year being due by April 30 of such year; with the return for April, May and June of a given year being due by July 31 of such year; with the return for July, August, and September of a given year being due by October 31 of such year; and with the return for October, November and December of a given year being due by January 31 of the following year.
If the average monthly tax liability of the self-assessing purchaser to the Department does not exceed $1,000, the Department may authorize the self-assessing purchaser's returns to be filed on an annual basis, with the return for a given year being due by January 31 of the following year.
Such quarter-annual and annual returns, as to form and substance, shall be subject to the same requirements as monthly returns.
Notwithstanding any other provision in this Law concerning the time within which a self-assessing purchaser may file a return, any such self-assessing purchaser who ceases to be responsible for filing returns under this Law shall file a final return under this Law with the Department not more than one month thereafter.
Each self-assessing purchaser whose average monthly liability to the Department pursuant to this Section was $10,000 or more during the preceding calendar year, excluding the month of highest liability and the month of lowest liability during such calendar year, and which is not operated by a unit of local government, shall make estimated payments to the Department on or before the 7th, 15th, 22nd and last day of the month during which tax liability to the Department is incurred in an amount not less than the lower of either 22.5% of such self-assessing purchaser's actual tax liability for the month or 25% of such self-assessing purchaser's actual tax liability for the same calendar month of the preceding year. The amount of such quarter-monthly payments shall be credited against the final tax liability of the self-assessing purchaser's return for that month. An outstanding credit approved by the Department or a credit memorandum issued by the Department arising from the self-assessing purchaser's overpayment of the self-assessing purchaser's final tax liability for any month may be applied to reduce the amount of any subsequent quarter-monthly payment or credited against the final tax liability of such self-assessing purchaser's return for any subsequent month. If any quarter-monthly payment is not paid at the time or in the amount required by this Section, such person shall be liable for penalty and interest on the difference between the minimum amount due as a payment and the amount of such payment actually and timely paid, except insofar as such person has previously made payments for that month to the Department in excess of the minimum payments previously due.
If the Director finds that the information required for the making of an accurate return cannot reasonably be compiled by a self-assessing purchaser within 15 days after the close of the calendar month for which a return is to be made, the Director may grant an extension of time for the filing of such return for a period of not to exceed 31 calendar days. The granting of such an extension may be conditioned upon the deposit by such self-assessing purchaser with the Department of an amount of money not exceeding the amount estimated by the Director to be due with the return so extended. All such deposits shall be credited against such self-assessing purchaser's liabilities under this Law. If the deposit exceeds such self-assessing purchaser's present and probable future liabilities under this Law, the Department shall issue to such self-assessing purchaser a credit memorandum, which may be assigned by such self-assessing purchaser to a similar person under this Law, in accordance with reasonable rules and regulations to be prescribed by the Department.
The self-assessing purchaser making the return provided for in this Section shall, at the time of making such return, pay to the Department the amount of tax imposed by this Law.
Until October 1, 2002, a self-assessing purchaser who has an average monthly tax liability of $10,000 or more shall make all payments required by rules of the Department by electronic funds transfer. The term "average monthly tax liability" shall be the sum of the self-assessing purchaser's liabilities under this Law for the immediately preceding calendar year divided by 12. Beginning on October 1, 2002, a taxpayer who has a tax liability in the amount set forth in subsection (b) of Section 2505-210 of the Department of Revenue Law shall make all payments required by rules of the Department by electronic funds transfer. Any self-assessing purchaser not required to make payments by electronic funds transfer may make payments by electronic funds transfer with the permission of the Department. All self-assessing purchasers required to make payments by electronic funds transfer and any self-assessing purchasers authorized to voluntarily make payments by electronic funds transfer shall make those payments in the manner authorized by the Department.
If any payment provided for in this Section exceeds the self-assessing purchaser's liabilities under this Act, as shown on an original return, the Department may authorize the self-assessing purchaser to credit such excess payment against liability subsequently to be remitted to the Department under this Act, in accordance with reasonable rules adopted by the Department.
Through June 30, 2004, each month the Department shall pay into the Public Utility Fund in the State treasury an amount determined by the Director to be equal to 3.0% of the funds received by the Department pursuant to this Section. Through June 30, 2004, the remainder of all moneys received by the Department under this Section shall be paid into the General Revenue Fund in the State treasury. Beginning on July 1, 2004, of the 3% of the funds received pursuant to this Section, each month the Department shall pay $416,667 into the General Revenue Fund and the balance shall be paid into the Public Utility Fund in the State treasury.
35 ILCS 640/2-11