Similar to the federal Schedule K-1, the purpose of Schedule K-1-P, Partner's or Shareholder's Share of Income, Deductions, Credits, and Recapture, is for partnerships and S corporations to supply each individual or entity who was a partner or shareholder at any time during the tax year with the information needed by the individual or entity to properly report the pass-through income on its Illinois Income Tax return.
For more information, please see Publication 129, Pass-through Entity Income.