The term "region," as used in this article, shall mean a specific metropolitan interstate area designated by the proper federal agency pursuant to the "Demonstration Cities and Metropolitan Development Act of 1966" and any amendments thereto, as well as all other interstate areas which would benefit from cooperative planning. Before any area in this state is included within an interstate region for interstate planning, it shall be approved by the Governor: Provided, That no territory within any municipality or county not having a planning commission shall be included in an interstate area.