(35 ILCS 5/904) (from Ch. 120, par. 9-904)

Sec. 904.

Deficiencies and Overpayments.

(a) Examination of return.  As soon as practicable after a return is
filed, the Department shall examine it to determine the correct amount of
tax. If the Department finds that the amount of tax shown on the return is
less than the correct amount, it shall issue a notice of deficiency to the
taxpayer which shall set forth the amount of tax and penalties proposed to
be assessed. If the Department finds that the tax paid is more than the
correct amount, it shall credit or refund the overpayment as provided by
Section 909. The findings of the Department under this subsection shall
be prima facie correct and shall be prima facie evidence of the correctness
of the amount of tax and penalties due.

(b) No return filed.  If the taxpayer fails to file a tax return, the
Department shall determine the amount of tax due according to its best
judgment and information, which amount so fixed by the Department shall be
prima facie correct and shall be prima facie evidence of the correctness of
the amount of tax due. The Department shall issue a notice of deficiency to
the taxpayer which shall set forth the amount of tax and penalties proposed
to be assessed.

(c) Notice of deficiency.  A notice of deficiency issued under this
Act shall set forth the adjustments giving rise to the proposed assessment
and the reasons therefor. In the case of a joint return, the notice of
deficiency may be a single joint notice except that if the Department is
notified by either spouse that separate residences have been established,
it shall issue joint notices to each spouse.

(d) Assessment when no protest.  Upon the expiration of 60 days after
the date on which it was issued (150 days if the taxpayer is outside the
United States), a notice of deficiency shall constitute an assessment of
the amount of tax and penalties specified therein, except only for such
amounts as to which the taxpayer shall have filed a protest with the
Department, as provided in Section 908.

(Source: P.A. 87-192; 87-205.)