35 ILCS 115/3-25
For the purposes of this Act, "computer software" means a set of statements, data, or instructions to be used directly or indirectly in a computer in order to bring about a certain result in any form in which those statements, data, or instructions may be embodied, transmitted, or fixed, by any method now known or hereafter developed, regardless of whether the statements, data, or instructions are capable of being perceived by or communicated to humans, and includes prewritten or canned software that is held for repeated sale or lease, and all associated documentation and materials, if any, whether contained on magnetic tapes, discs, cards, or other devices or media, but does not include software that is adapted to specific individualized requirements of a purchaser, custom-made and modified software designed for a particular or limited use by a purchaser, or software used to operate exempt machinery and equipment used in the process of manufacturing or assembling tangible personal property for wholesale or retail sale or lease. Software used to operate machinery and equipment used in (i) the generation of electricity for wholesale or retail sale; (ii) the generation or treatment of natural or artificial gas for wholesale or retail sale that is delivered to customers through pipes, pipelines, or mains; or (iii) the treatment of water for wholesale or retail sale that is delivered to customers through pipes, pipelines, or mains is considered "computer software". The provisions of this amendatory Act of the 98th General Assembly are declaratory of existing law as to the meaning and scope of this exemption.
For the purposes of this Act, computer software shall be considered to be tangible personal property.
35 ILCS 115/3-25