For my home state of IL, the grid is pretty much on par with several other states, with most routes taking a fairly straight path, with the lone exception being the crooked IL 110, which is always multiplexed with others, including I-88 and I-290. Its US highways are neat parallels to the Interstates they complement, even without US 66. Plus I like how IL 1 stretches from Chicago to the other end of the state.
The Single Digit IL State Routes tend to have a bit of significance
IL 1 was already mentioned, and a bonus: the northern third of the route is also essentially the old Dixie Highway routing in IL
IL 2 runs along the Rock River between Rockford and Sterling
IL 3 is a significant route in SW IL, from Cairo near the confluence of the Ohio and the Mississippi, up into and thru the Metro East, ending at Grafton near the confluence of the Illinois and the Mississippi
IL 4 historically was a Chicago-St Louis predecessor highway to what became US 66 and then I-55. The current route encompasses past of the historical routing between Springfield and Staunton, then making a de facto outer Metro East/STL eastern bypass, and the 4 number continues south into Jackson County and ends north of Murphysboro
IL 5 used to be the then-East-West now Reagan Tollway/I-88, and still exists as a major roadway in the Quad Cities area
IL 6 is the designation of the part of the Peoria Beltway Freeway north of I-74
IL 7 is a major highway in the Southwest Chicago Suburbs, going from Rockdale and Joliet to Harlem Ave/IL 43 near the Chicago City Limits. IL 7 is aptly named Southwest Highway for much of its length
IL 8 is shorter, but crosses the IL River in Peoria and is an important route in that part of the state
IL 9 successfully runs Indiana to Iowa across Central Illinois, meeting IN 26 to the east, and crossing the Mississippi to reach Business US 61 in Fort Madison, IA
Regarding IL 110, either it or IL 336 should be decommissioned. The would-be independent section of IL 336 between Macomb and Peoria is either officially or unofficially cancelled, and 110 and 336 are 100% multiplexed with each other. Every inch of 336 is also 110