35 ILCS 110/6
A serviceman maintaining a place of business in this State, if required to register under the Retailers' Occupation Tax Act, or under the Use Tax Act, or under the Service Occupation Tax Act, need not obtain an additional Certificate of Registration under this Act, but shall be deemed to be sufficiently registered by virtue of his being registered under the Retailers' Occupation Tax Act, or under the Use Tax Act, or under the Service Occupation Tax Act. Every serviceman maintaining a place of business in this State, if not required to register under the Retailers' Occupation Tax Act, or under the Use Tax Act, or under the Service Occupation Tax Act, shall apply to the Department (upon a form prescribed and furnished by the Department) for a Certificate of Registration under this Act. In completing such application, the applicant shall furnish such information as the Department may reasonably require. Upon approval of an application for Certificate of Registration, the Department shall issue, without charge, a Certificate of Registration to the applicant. Such Certificate of Registration shall be displayed at the address which the applicant states in his application to be the principal place of business or location from which he will act as a serviceman in this State. If the applicant will act as a serviceman in this State from other places of business or locations, he shall list the addresses of such additional places of business or locations in his application for Certificate of Registration, and the Department shall issue a Sub-Certificate of Registration to the applicant for each such additional place of business or location. Each Sub-Certificate of Registration shall be conspicuously displayed at the place for which it is issued. Such Sub-Certificate of Registration shall bear the same registration number as that appearing upon the Certificate of Registration to which such Sub-Certificates relate. Where a serviceman operates more than one place of business which is subject to registration under this Section and such businesses are substantially different in character or are engaged in under different trade names or are engaged in under other substantially dissimilar circumstances (so that it is more practicable, from an accounting, auditing or bookkeeping standpoint, for such businesses to be separately registered), the Department may require or permit such person to apply for and obtain a separate Certificate of Registration for each such business or for any of such businesses instead of registering such person, as to all such businesses, under a single Certificate of Registration supplemented by related Sub-Certificates of Registration. No Certificate of Registration shall be issued to any person who is in default to the State of Illinois for moneys due hereunder.
35 ILCS 110/6