There is little literature on documenting the correct application of classification systems. This paper seeks to remedy this gap by describing how Northeastern Illinois University created documentation for their implementation of system that describes Illinois State publications. We recommend creating documentation that is flexible, accessible, and user-oriented. Flexible documentation not only facilitates changes to the documentation, it also allows librarians to take advantage of other uses of this documentation. In our case, the process of documentation produced a near complete listing of Illinois publications and provided the basis for a structural history of Illinois government. Documentation of classification systems not only improves library work, but also assists in preserving artifacts of library history.