History
SBI Route 64 was Illinois 64 from Sycamore to Chicago. In 1937 it was extended west to what was then U.S. Route 51 (and is now Illinois Route 251). Afterwards, it was extended further west to U.S. Route 52, and then following it to the state line. Much like Illinois Route 92, there is no particular reason for extending Route 64 through Iowa and Nebraska, as existing U.S. Routes served any major cities on the State Route 64s better.
Read more about this topic: Illinois Route 64