I never understood why Peoria is the control city for I-74 westbound. I'd think Champaign/Urbana (intersection of I-57 and I-72) or Bloomington/Normal (intersection of I-55 and I-39) would be more appropriate, since there is no major Interstate highway intersection at Peoria and both the above examples are decent-sized cities.
Probably because back when control cities were being decided, Blormal and Chambana weren't as big as Peoria. From Wikipedia
* Population of Peoria in 1950: 111,856
* Population of Peoria in 1960: 103,162 (though it's up to 126,963 in 1970)
* Population of Bloomington in 1950: 34,163
* Population of Bloomington in 1960: 36,274
* Population of Normal in 1950: 9,772
* Population of Normal in 1960: 13,357
* Population of Champaign in 1950: 39,563
* Population of Champaign in 1960: 49,583
* Population of Urbana is unfortunately not available for most years, but the 2010 population was 41,250
Also back in the early days both areas would not have been as important of junctions since neither I-72 nor I-39 were part of the original interstate plans; I-57 and I-55 are kind of double back routes in a sense that long distance interstate traffic (such as motorist going from Indianapolis to Chicago and beyond) would not change to those other interstates.