That's really a question of "what does IL law require," and I have no clue there. For my big multi-state returns, I figure the correct answer in Excel and make Lacerte agree, mostly because the -1 errors add up.  My best guess is that you need entries in both the State if Different and State Source columns for each K-1, but even then, you might need to judiciously override. The more K-1s and the more states, the less able you are to rely on Lacerte producing exactly the right output, even if you know what exactly the right input is.