The 100^th anniversary of the publication of W. S. Blatchley's An Illustrated Descriptive Catalogue of the Coleoptera or Beetles (Exclusive of the Rhynchophora) Known to Occur in Indiana is observed. Reasons behind this classic monograph's enduring utility are explored. In addition, the volume's origin, projected audience, and relationships to later identification manuals are examined, along with Blatchley's other major entomological contributions. Blatchley's Coleoptera in Indiana became a model for several regional studies and was not superseded for close to 90 years.