The Post Office Department of the United States was founded by the Continental Congress in 1775. As a result of its lengthy history, post offices are the most common civic building type in the nation. The nationwide decline in postal services caused by decreased foot traffic and the rise of outside competition, primarily driven by E-commerce, has destabilized the self-sufficient nature of postal institutions, leaving a large inventory of underutilized historic postal properties. The Allentown Post Office has continuously served as a post office since its inception in 1934. In 2018, the United States Postal Service desired a reduction in the footprint of their postal operations, citing the steady decline in community postal services. Hence, local advocates have spent the last six years in the commercial real estate market, looking for a new purpose. In order to save the historic postal inventory, the buildings need to be assigned a new purpose through adaptive reuse. The problem is, too many adaptive reuse projects practice rehabilitations that conserve the exterior only to strip the interior of its finishes, partitions, and spatial relationships. The Allentown Post Office case study explored adaptive reuse principles through a preservation lens where both exterior and interior historic features are retained and repaired rather than modified and replaced. The Allentown Post Office case study established its historic significance through the development of the local community, postal services, transportation methods, setting, siting, interior and exterior architecture, its material conditions, and treatment recommendations. A reuse feasibility study followed, and suggested the historic integrity of the building can be preserved by creative and selective tenancy as a commercial mixed-use property, including warehousing, banking, and office spaces as an economically viable proposal. The reuse proposal for the Allentown Post Office served as a template to be applied to other post offices in the national building stock looking to economize and preserve their architectural heritage.