I have a W-2 for US Railroad Retirement Board Sickness and Unemployment Benefits with Gross Wages in Box 1.  Box 13 has "Third Party Sick Pay" box checked.  There is Nothing in the State boxes 15, 16 and 17.  Is this item Taxable in the state of Illinois?  Should I include it as a Schedule M subtraction item line 35. Has anyone seen this before?  Thank you for any assistance.