Indiana Code Title 6. Taxation § 6-8.1-1-9

Sec. 9. (a) If any due date or date required for a particular act by the taxpayer or the department falls on Saturday, Sunday, a national legal holiday recognized by the federal government, or a statewide holiday, the act by the taxpayer or the department that must be performed by that date is timely if performed by the next succeeding day that is not a Saturday, a Sunday, or one of those holidays.

(b) If the due date of a particular act is later than the date otherwise provided for the act as a result to the due date falling on Saturday, Sunday, a national legal holiday recognized by the federal government, or a statewide holiday, the last date on which a proposed assessment or demand notice must be issued or the last day on which a refund claim may be filed shall be determined without regard to the original due date (including allowable extensions) falling on a Saturday, Sunday, or holiday.