(35 ILCS 5/505) (from Ch. 120, par. 5-505)
    Sec. 505. Time and Place for Filing Returns. (a) In general. Returns required by this Act shall be filed at such place as the Department may by regulations prescribe.
    (1) Corporations. Except as provided in paragraph (3), corporate returns shall be filed on or before the 15th day of the third month following the close of the taxable year, unless, subject to the provisions of Section 602, the Director grants an extension or extensions of time (not to exceed 6 months in the aggregate) for such filing, or unless the income or loss of a taxpayer is reported for federal purposes on a return with a due date later than the 15th day of the third month following the close of the taxable year, in which case the same due date shall apply to the corresponding Illinois return.
    (2) Individuals, partnerships and fiduciaries. Except as provided in paragraph (3), individual, partnership and fiduciary returns shall be filed on or before the 15th day of the fourth month following the close of the taxable year, unless, subject to the provisions of Section 602, the Director grants an extension or extensions of time (not to exceed 6 months in the aggregate) for such filing, except that a final return of a decedent shall be filed at the time (including any extensions thereof) it would have been due if the decedent had not died.
    (3) Certain Exempt Organizations. Organizations which are exempt from the Federal income tax by reason of Section 501(a) of the Internal Revenue Code who determine base income for a taxable year under subsection (a) of Section 205 (other than an employees' trust described in Section 401(a) of the Internal Revenue Code), shall file returns required by this Act on or before the 15th day of the 5th month following the close of the taxable year, unless, subject to the provisions of Section 602, the Director grants an extension or extensions of time (not to exceed 6 months in the aggregate) for such filing.
    (b) Extension of time for filing federal return. When the taxpayer has been granted an extension or extensions of time within which to file his federal income tax return for any taxable year, the filing of a copy of such extension or extensions with the Department shall automatically extend the due date of the return with respect to the tax imposed by this Act for an equivalent period (plus an additional month beyond the federal extension in the case of corporations) if the requirements of Section 602 are met.
    (c) Extension of time for filing when abroad. If an individual is living or traveling outside the United States and Puerto Rico on the 15th day of the 4th month following the close of his taxable year ending on or after December 31, 1983, the return required to be filed under Section 502 of this Act relative to that taxable year shall, in no event, be due prior to the 15th day of the 6th month following the close of that taxable year. In the case of a joint return filed in accordance with Section 502(c), the 2 month extension provided for in this subsection (c) is available if either spouse is living or traveling outside the United States and Puerto Rico on the 15th day of the 4th month following the close of the taxable year ending on or after December 31, 1983. Nothing in this subsection (c) shall be construed to extend the time in which the individual must pay the tax due under Section 601(a).
(Source: P.A. 84-1400.)