After the establishment of a regional library as provided for in this act, the township board, the legislative body of any city or village, the board of education of any school district or the board of supervisors of any municipality in the region, already maintaining a public, school or county library, may notify the board of trustees of the regional library that such township, city, village, school district or county library may be transferred to, leased to, or used by said board of trustees of the regional library under such terms as may mutually be agreed upon between the said board of trustees and the respective township boards, city or village legislative bodies, boards of education or boards of supervisors.