Each district library commission shall be composed of 5 members who are residents of the school district in which the public library is established. The 5 members serving on any such district library commission as of July 1, 1975, shall continue in office until the expiration of the terms for which they were appointed. Upon the expiration of the term of any member, such member's successor shall be appointed by the Resident Judge of the Superior Court of the State for the county in which the school district is located for a term of 5 years. In case a district is located partly in each of 2 counties, the appointments to fill vacancies caused by expiration of a term shall be made alternately from the 2 counties by the Resident Judge of the county in which the greater number of residents of the school district reside. Appointment to fill an unexpired term is not to be considered a complete term. Each member shall hold office until the member's successor is appointed and qualified. Any vacancy in the membership of the commission shall be filled by the Resident Judge for the unexpired portion of the 5 year term.