South Dakota Codified Law (SDCL) 14-2-35 provides that "Any public library established under subdivision § 14-2-29(1)shall be governed by a board of public library trustees." Although the foregoing SDCL quote establishes the existence of the public library trustee board, it fails to answer the question, "Why are trustees necessary in small libraries ... or even in large libraries?"
The public library, dependent as it is on the community, needs library boards as citizen representatives to ensure that the public library is a true reflection of the community. Board members, as representatives of the community, are of vital assistance to the librarian as barometers of change in the community which will alter the role of the library. Board members bring the community's voice into the deliberations leading to library planning and policy making. Being responsible to the community as its’ designated representative, board members ensure that the library provides the best possible affordable library service for the community.
It is the trustee's obligation to improve the library through well trained staff and efficient use of funds, to obtain adequate funds for good library services, to promote the best possible use of all library resources in the area and to extend library services to those not previously served.
STATE LIBRARY DEFINITION OF ADEQUATE LIBRARY SERVICE this whole definition was repealed in 1998. Do we need something different, or just delete?

Rules of the South Dakota Department of Education, Division of the State Library:
Section 24:30:01:02. ... a public library is considered inadequate if it is not open to the public at least forty hours a week including at least two nights and a period of time on Saturday; if it has no telephone; if it is not staffed with at least one person holding a bachelor's degree from an accredited institution of higher education, or having two years of college and six hours of college credit in librarianship or twelve library continuing education units, or having two years of college and two years of library experience, or having a high school diploma and twelve hours of college credit in librarianship or twenty-four library continuing education units or an equivalent combination of college credits in librarianship and library continuing education units; if it is more than ten miles distant from a citizen's place of residence or business; if it purchases less than five hundred books per annum; and if it does not purchase the minimum quantity of book and periodical indexes recommended by the state library.
(The state library uses the above definition as a determining factor in providing access for patron usage of state library service. The definition should not be considered mandatory or complete in any other application.)