You probably do need to file. It is not true that you don't need to file if you made under $10,000.
An Illinois resident, you must file Form IL-1040 if
you were required to file a federal income tax return, or
you were not required to file a federal income tax return, but your Illinois base income from Line 9 is greater than your Illinois exemption allowance.
The exemption amounts vary on your filing status and income and go from a low of $2250 to $4450. See below page 8:
