ILLINOIS INTERSTATE ROUTE NUMBERING
On August 14, 1957 AASHO releases the Preliminary Interstate Route Numbering Plan for Illinois as Follows:
I-55: St.Louis thru Springfield and Bloomington onto Chicago
I-57: Cairo thru Effingham onto Chicago
I-64: St. Louis Due east to IL/IN state line
I-70: St. Louis thru Effingham onto IL/IN state line
I-74: Moline Southeastward thru Bloomington onto IL/IN state line
I-80: Moline Due East thru South Suburbs of Chicago onto IL/IN state line
I-90: WI/IL state line  Southeastward thru Chicago onto IL/IN state line
I-94: WI/IL state line due South thru Chicago onto IL/IN state line

On July 2, 1958 AASHO adds the following route:
I-24: I-57 in far Southern Illinois in a Southeast direction to KY/IL state line

On July 24, 1958 The Illinois Division of Highways submitted there Urban Numbering Plan to AASHO as follows:
Chicago:
I-294: I-94 NW of Chicago following Tri-State Tollway then Multiplexing with I-80 and I-90 into Indiana
I-494: Lake Shore Loop
MAP
Peoria:
I-474: Peoria West Loop
Quad Cities:
I-274: Quad Cities East Loop
I-280: Quad Cities Southwest Loop
St. Louis Suburban:
I-255: St. Louis Southeast Loop
I-270: St. Louis Northern Loop

On November 10, 1958 the Interstate System Route Numbering was approved by AASHO as follows:
I-24: I-57 in far Southern Illinois in a Southeast direction to KY/IL state line
I-55: St.Louis thru Springfield and Bloomington onto Chicago
I-57: Cairo thru Effingham onto Chicago
I-64: St. Louis Due east to IL/IN state line
I-70: St. Louis thru Effingham onto IL/IN state line
I-74: Moline Southeastward thru Bloomington onto IL/IN state line
I-80: Moline Due East thru South Suburbs of Chicago onto IL/IN state line
I-90: WI/IL state line  Southeastward thru Chicago onto IL/IN state line
I-94: WI/IL state line due South thru Chicago onto IL/IN state line
Chicago:
I-294: I-94 NW of Chicago following Tri-State Tollway then Multiplexing with I-80 and I-90 into Indiana
I-494: Lake Shore Loop
MAP
Peoria:
I-474: Peoria West Loop
Quad Cities:
I-274: Replace with rerouted I-80
I-280: Quad Cities Southwest Loop
Map Follows:
MAP
St. Louis Suburban:
I-255: St. Louis Southeast Loop
I-270: St. Louis Northern Loop