26 CFR § 20.6091-1 - Place for filing returns or other documents.
(a) General rule. If the decedent was domiciled in the United States at the time of his death, the preliminary notice required by § 20.6036-1 in the case of the estate of a decedent dying before January 1, 1971, and the estate tax return required by § 20.6018-1 shall be filed with:
(1) The service center serving the location in which the decedent was domiciled at the time of his death, if the instructions applicable to the estate tax return provide that the return shall be filed with a service center, or
(2) Any person assigned the responsibility to receive returns in the local Internal Revenue Service office serving the location in which the decedent was domiciled at the time of his death, if paragraph (a)(1) of this section does not apply.
(b) Non-U.S. domiciliaries. If the decedent was not domiciled in the United States at the time of his death, the preliminary notice required by § 20.6036-1 in the case of the estate of a decedent dying before January 1, 1971, and the estate tax return required by § 20.6018-1 shall be filed with the Internal Revenue Service Center, Philadelphia, Pa. or as designated on the return form or in the instructions issued with respect to such form. This paragraph applies whether or not the decedent was a citizen of the United States and whether or not the return is made by hand-carrying.