Indiana Code Title 23. Business and Other Associations § 23-17-12-7

Sec. 7. (a) A director may resign at any time by delivering written notice to one (1) of the following:

(b) A resignation is effective when the notice is effective under IC 23-17-28 unless the notice specifies a later effective date.  If a resignation is made effective at a later date, the board of directors may fill the pending vacancy before the effective date if the board of directors provides that the successor does not take office until the effective date.