
Quoting
625 ILCS 5/11-601(d)
(d) Unless some other speed restriction is established under this Chapter, the maximum speed limit outside an urban district for any vehicle of the first division or a second division vehicle designed or used for the carrying of a gross weight of 8,000 pounds or less (including the weight of the vehicle and maximum load) is (1) 65 miles per hour (i) for all highways under the jurisdiction of the Illinois State Toll Highway Authority and (ii) for all or part of highways that are designated by the Department, have at least 4 lanes of traffic, and have a separation between the roadways moving in opposite directions and (2) 55 miles per hour for all other highways, roads, and streets.