35 ILCS 120/2c
If the purchaser is not registered with the Department as a taxpayer, but claims to be a reseller of the tangible personal property in such a way that such resales are not taxable under this Act or under some other tax law which the Department may administer, such purchaser (except in the case of an out-of-State purchaser who will always resell and deliver the property to his customers outside Illinois) shall apply to the Department for a resale number. Such applicant shall state facts which will show the Department why such applicant is not liable for tax under this Act or under some other tax law which the Department may administer on any of his resales and shall furnish such additional information as the Department may reasonably require.
Upon approval of the application, the Department shall assign a resale number to the applicant and shall certify such number to him. The Department may cancel any such number which is obtained through misrepresentation, or which is used to make a purchase tax-free when the purchase in fact is not a purchase for resale, or which no longer applies because of the purchaser's having discontinued the making of tax exempt resales of the property.
The Department may restrict the use of the number to one year at a time or to some other definite period if the Department finds it impracticable or otherwise inadvisable to issue such numbers for indefinite periods.
Except as provided hereinabove in this Section, a sale shall be made tax-free on the ground of being a sale for resale if the purchaser has an active registration number or resale number from the Department and furnishes that number to the seller in connection with certifying to the seller that any sale to such purchaser is nontaxable because of being a sale for resale. On and after January 1, 2025, a sale to a lessor of tangible personal property who is subject to the tax on leases implemented by this amendatory Act of the 103rd General Assembly, for the purpose of leasing that property, shall be made tax-free on the ground of being a sale for resale, provided the other provisions of this paragraph are met.
Failure to present an active registration number or resale number and a certification to the seller that a sale is for resale creates a presumption that a sale is not for resale. This presumption may be rebutted by other evidence that all of the seller's sales are sale for resale, or that a particular sale is a sale for resale.
35 ILCS 120/2c