To facilitate discovery of premodern manuscripts in U.S. memory institutions, Digital Scriptorium, a growing consortium of over 35 institutional members representing American libraries, museums, and other cultural heritage institutions, has developed a digital platform for an online national union catalog. The platform will allow low-barrier and efficient collection, aggregation, and enrichment of member metadata and sustainably publish it as Linked Open Data. This article describes the methods and principles behind the data model development and the decision to use Wikibase. The results of the prototype implementation and testing phase demonstrate the practicality and sustainability of Digital Scriptorium’s approach to building an online national union catalog based on Linked Open Data technologies and practices.