Based on your facts:
- Unless you made a Section 444 election, your required year end is most likely December
- You need to fix the year end mistakes with both the IRS and IL
- I would not do anything with how you filed the current year form 1065 as I believe that is filed correctly.
- I recommend that you meet with a tax professional after April 15th and have them help you get this corrected as noted in circle 2 above.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
