Indiana Code Title 36. Local Government § 36-7-4-220

Sec. 220. (a) If a vacancy occurs among the plan commission members who are appointed, then the appointing authority shall appoint a member for the unexpired term of the vacating member who meets the same requirements as the vacating member, including residency, not later than ninety (90) days after the vacancy occurs.  The appointing authority may also appoint an alternate member who meets the same requirements as the disqualified member, including residency, to participate with the commission in a hearing or decision if the regular member appointed by the appointing authority has a disqualification under section 223(c) of this chapter.  An alternate member has all the powers and duties of a regular member while participating in the hearing or decision.

(b) If a vacancy occurs in the office of the county surveyor while the county surveyor is serving on the plan commission, then the county engineer shall participate with the plan commission during the time the office of the county surveyor is vacant.  The county engineer has all the powers and duties of a regular member while participating under this subsection.

(c) An appointed member who misses three (3) consecutive regular meetings of the plan commission may be treated as if the member had resigned, at the discretion of the appointing authority.