An independent library needs at least one full-time employee according to the regulation §141.21(2)(iv)(d) - "The library must have one qualified staff member or full time equivalent (FTE) for each 3,500 persons in its direct service area. The library must have at least one (1) full time staff member (35 hours/week). If there is only one (1) full time staff member, that person must be certified at least as a Library Assistant."
Historically, system member libraries have not been held accountable for meeting this standard and because of this, the standard only applies to independent libraries.