I am an Indian citizen and did internship at Northwestern University(period May 13, 2012-August 4, 2012) which is in Illinois.
According to my W-2 state taxes have been deducted from the wages I received. I need to file a tax return. Which form should I file. According to me(from the reading) I should file just IL-1040 only. Am I correct.

If I am to file IL 1040, then what information I should provide in Spouse's related section(fields like Spouse SSN etc.). I am single.

Any help appreciated.

Thanks in advance.

You file as a SINGLE non-resident. Leave all SPOUSE information blank.