510 ILCS 30/6.1
The Department may require that no dairy or breeding cattle more than 6 months of age shall be shipped from any livestock auction markets or marketing centers in Illinois consigned to any point within the State unless they are accompanied by a certificate of health issued by an accredited veterinarian or a veterinarian employed by the Animal and Plant Health Inspection Service of the United States Department of Agriculture, or any successor agency, showing them to have been negative to an official test for brucellosis prior to release from such public stockyards or be under 24 months of age for beef breeds and 20 months of age for dairy breeds and accompanied by a record of official brucellosis calfhood vaccination.
Cattle consigned to livestock auction markets or marketing centers in Illinois may enter such livestock auction markets or marketing centers without test or certificates of health showing them to be free from brucellosis, however, the Department may require that these animals must be negative to an official test for brucellosis before they are removed to an Illinois farm.
510 ILCS 30/6.1