Charles Adam Platt (1861-1933) was an American architect and landscape designer. Although best remembered today for his landscape and country house designs, he was also nationally known for his etchings, landscape paintings, commercial architecture, and institutional projects. He was largely self-taught in each of these disciplines, building his success on his ability to reconceive the classical tradition in architecture for the needs and desires of his wealthy, powerful clients. This collection contains materials related to Platt's personal and professional lives, the bulk originating from Platt's office in the form of project drawings, photographs, and records documenting architectural projects from 1901-1933.

This collection contains primarily project records, including drawings, files, specifications, correspondence, and photographs, related to the architectural practice of William & Geoffrey Platt. Projects including commercial, institutional, and residential buildings located in Colorado, Connecticut, Delaware, Florida, Louisiana, Massachusetts, Maine, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Virginia, Vermont, Washington, and France. The firm was involved in the design of many buildings and additions for institutions such as the Pierpoint Morgan Library, Princeton University, Smith College, and Deerfield Academy.