Alexander McMillan Welch (1869-1943) was a New York City based architect who practiced independently and as a member of Welch, Smith & Provot. His firm was best known for designing New York City townhouses in the Beaux-Arts style. The collection includes 1,641 architectural drawings, 196 student drawings, 14 student notebooks, 99 loose photographs and 3 photo albums of project photography, project specifications and files, and some professional ephemera.

Architectural plans and renderings of Welch's designs, largely New York City residences, circa 1890s-1920s; specifications; photographs; and brochures advertising buildings at 787 Fifth Ave., 628 Fifth Ave., and 71 and 73 Murray Street, in New York City. Drawings and a sketchbook done by Welch while a student; fourteen notebooks containing Welch's notes from Columbia classes in architecture, 1888-1890; licenses to practice in New York and New Jersey, 1904-1923; a certificate, 1937, and related correspondence relating to Welch's appointment as a U.S. delegate to the fourteenth International Congress of Architects, held in Paris, July 18-25, 1937. A list of U.S. delegates is included. Of note are drawings and papers for the restoration of the Dyckman House, an 18th century farmhouse in upper Manhattan (1910-1917); and the Mrs. Rutherford Stuyvesant Estate in Allamuchy, New Jersey, and the Rutherford Stuyvesant Momument in Tranquility Cemetery, Tranquility, New Jersey, designed by sculptor Daniel Chester French.

Papers consist primarily of Smith's files relating to his architectural work containing correspondence with clients, colleagues, contractors, suppliers, and others, with related bills, notes, receipts, accounts, estimates, specifications, time sheets, progress reports, and architectural drawings. Also, portrait photographs of young people (possibly classmates?) in Rochester, N.Y. and Evanston, Ill., circa late 19th century; a class roll card, 1901, for a class taught by Smith at the General Society of Mechanics and Tradesmen, New York; a memo book, undated, containing miscellaneous accounts, sketches, memoranda; correspondence, 1890s, between Ella Smith (Smith's mother) and Lucien Smith and other family members, Rochester, N.Y., and Elmhurst, Ill.; account book, 1891-1902, of Mrs. H. V. (Ella) Smith, Rochester, N.Y.; calling cards, invitations, photographs, letters, bills, receipts, and other, miscellaneous personal documents; student drawings made by Smith when at Columbia University's School of Architecture; drawings for a proposed "academy of art and archaeology" in Rome, 1905-1906; and drawings for Malvina Hoffman's house and studio in New York City.