35 ILCS 120/6
If it appears, after claim therefor filed with the Department, that an amount of tax or penalty or interest has been paid which was not due under this Act, whether as the result of a mistake of fact or an error of law, except as hereinafter provided, then the Department shall issue a credit memorandum or refund to the person who made the erroneous payment or, if that person died or became a person under legal disability, to his or her legal representative, as such. For purposes of this Section, the tax is deemed to be erroneously paid by a retailer when the manufacturer of a motor vehicle sold by the retailer accepts the return of that automobile and refunds to the purchaser the selling price of that vehicle as provided in the New Vehicle Buyer Protection Act. When a motor vehicle is returned for a refund of the purchase price under the New Vehicle Buyer Protection Act, the Department shall issue a credit memorandum or a refund for the amount of tax paid by the retailer under this Act attributable to the initial sale of that vehicle. Claims submitted by the retailer are subject to the same restrictions and procedures provided for in this Act. If it is determined that the Department should issue a credit memorandum or refund, the Department may first apply the amount thereof against any tax or penalty or interest due or to become due under this Act or under the Use Tax Act, the Service Occupation Tax Act, the Service Use Tax Act, any local occupation or use tax administered by the Department, Section 4 of the Water Commission Act of 1985, subsections (b), (c) and (d) of Section 5.01 of the Local Mass Transit District Act, or subsections (e), (f) and (g) of Section 4.03 of the Regional Transportation Authority Act, from the person who made the erroneous payment. If no tax or penalty or interest is due and no proceeding is pending to determine whether such person is indebted to the Department for tax or penalty or interest, the credit memorandum or refund shall be issued to the claimant; or (in the case of a credit memorandum) the credit memorandum may be assigned and set over by the lawful holder thereof, subject to reasonable rules of the Department, to any other person who is subject to this Act, the Use Tax Act, the Service Occupation Tax Act, the Service Use Tax Act, any local occupation or use tax administered by the Department, Section 4 of the Water Commission Act of 1985, subsections (b), (c) and (d) of Section 5.01 of the Local Mass Transit District Act, or subsections (e), (f) and (g) of Section 4.03 of the Regional Transportation Authority Act, and the amount thereof applied by the Department against any tax or penalty or interest due or to become due under this Act or under the Use Tax Act, the Service Occupation Tax Act, the Service Use Tax Act, any local occupation or use tax administered by the Department, Section 4 of the Water Commission Act of 1985, subsections (b), (c) and (d) of Section 5.01 of the Local Mass Transit District Act, or subsections (e), (f) and (g) of Section 4.03 of the Regional Transportation Authority Act, from such assignee. However, as to any claim for credit or refund filed with the Department on and after each January 1 and July 1 no amount of tax or penalty or interest erroneously paid (either in total or partial liquidation of a tax or penalty or amount of interest under this Act) more than 3 years prior to such January 1 and July 1, respectively, shall be credited or refunded, except that if both the Department and the taxpayer have agreed to an extension of time to issue a notice of tax liability as provided in Section 4 of this Act, such claim may be filed at any time prior to the expiration of the period agreed upon. Notwithstanding any other provision of this Act to the contrary, for any period included in a claim for credit or refund for which the statute of limitations for issuing a notice of tax liability under this Act will expire less than 6 months after the date a taxpayer files the claim for credit or refund, the statute of limitations is automatically extended for 6 months from the date it would have otherwise expired.
No claim may be allowed for any amount paid to the Department, whether paid voluntarily or involuntarily, if paid in total or partial liquidation of an assessment which had become final before the claim for credit or refund to recover the amount so paid is filed with the Department, or if paid in total or partial liquidation of a judgment or order of court. No credit may be allowed or refund made for any amount paid by or collected from any claimant unless it appears (a) that the claimant bore the burden of such amount and has not been relieved thereof nor reimbursed therefor and has not shifted such burden directly or indirectly through inclusion of such amount in the price of the tangible personal property sold by him or her or in any manner whatsoever; and that no understanding or agreement, written or oral, exists whereby he or she or his or her legal representative may be relieved of the burden of such amount, be reimbursed therefor or may shift the burden thereof; or (b) that he or she or his or her legal representative has repaid unconditionally such amount to his or her vendee (1) who bore the burden thereof and has not shifted such burden directly or indirectly, in any manner whatsoever; (2) who, if he or she has shifted such burden, has repaid unconditionally such amount to his own vendee; and (3) who is not entitled to receive any reimbursement therefor from any other source than from his or her vendor, nor to be relieved of such burden in any manner whatsoever. No credit may be allowed or refund made for any amount paid by or collected from any claimant unless it appears that the claimant has unconditionally repaid, to the purchaser, any amount collected from the purchaser and retained by the claimant with respect to the same transaction under the Use Tax Act.
Any credit or refund that is allowed under this Section shall bear interest at the rate and in the manner specified in the Uniform Penalty and Interest Act.
In case the Department determines that the claimant is entitled to a refund, such refund shall be made only from the Aviation Fuel Sales Tax Refund Fund or from such appropriation as may be available for that purpose, as appropriate. If it appears unlikely that the amount available would permit everyone having a claim allowed during the period covered by such appropriation or from the Aviation Fuel Sales Tax Refund Fund, as appropriate, to elect to receive a cash refund, the Department, by rule or regulation, shall provide for the payment of refunds in hardship cases and shall define what types of cases qualify as hardship cases.
If a retailer who has failed to pay retailers' occupation tax on gross receipts from retail sales is required by the Department to pay such tax, such retailer, without filing any formal claim with the Department, shall be allowed to take credit against such retailers' occupation tax liability to the extent, if any, to which such retailer has paid an amount equivalent to retailers' occupation tax or has paid use tax in error to his or her vendor or vendors of the same tangible personal property which such retailer bought for resale and did not first use before selling it, and no penalty or interest shall be charged to such retailer on the amount of such credit. However, when such credit is allowed to the retailer by the Department, the vendor is precluded from refunding any of that tax to the retailer and filing a claim for credit or refund with respect thereto with the Department. The provisions of this amendatory Act shall be applied retroactively, regardless of the date of the transaction.
35 ILCS 120/6