Taking a look at all the ratings systems through week 4:
https://masseyratings.com/ranks?s=cf&sub=10678
Based on the ratings composite, here are the B1G rankings:
1. Ohio State (5th overall)
2. Oregon (6th overall)
3. Penn State (8th overall)
4. Michigan (11th overall)
5. USC (16th overall)
6. Iowa (23rd overall)
7. Washington (27th overall)
8. Illinois (28th overall)
9. Indiana (31st overall)
10. Maryland (32nd overall)
11. Rutgers (34th overall)
12. Nebraska (42nd overall)
13. Wisconsin (47th overall)
14. MSU (55th overall)
15. Minnesota (64th overall)
16. Northwestern (75th overall)
17. UCLA (82nd overall)
18. Purdue (92nd overall)
Basically, 3 teams in a top tier "get a playoff bye", 2 other teams in a "in good position for a playoff spot", 6 teams in "looking forward to bowl season", 3 teams in "could get a bowl", and 4 in a "how's recruiting for next year looking" tier.
As for Illinois specifically, their ratings range from a high of 12th to a low of 56th. Significant improvements from their preseason ratings, which went as low as 126th (that rating now has them 38th). If they keep winning the games they should win and being competitive in these 3 upcoming tough games, they'll hover between 20 and 30 overall, which seems about right.
They currently have a 9% chance of making the playoffs according to ESPN, mostly due to their rough schedule (Indiana has about double that, since they only get 2 games against ranked teams, and they're late in the season). Probably need a 3-1 stretch in the next 4 to be in the playoff conversation afterwards, but the back quarter of their schedule should offer enough chances to pick up the wins they need for a bowl easy, and maybe look at an 8-4 or 9-3 season.