Indiana Code Title 36. Local Government § 36-7-4-204

Sec. 204. AREA.  After the planning department is established, other municipalities within the county may adopt ordinances adopting the area planning law and provide for the appointment of their representatives to the area plan commission.  In such a case, the membership of the commission shall be increased according to the formula provided in sections 207, 208, 209, and 211 of this chapter and the authority of a municipal plan commission and municipal board of zoning appeals ceases, except as provided in section 901(i) of this chapter, as of the time specified in that ordinance.  The composition of any such municipal board of zoning appeals, or of any such board later organized, under the advisory planning law, must conform with that law, except that those members of such a board to be appointed from the municipal plan commission shall instead be appointed from the area plan commission.