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.

Architectural drawings and photographs of architectural drawings with some related correspondence of residential and public buildings, churches, libraries, theaters, monuments, and bridges including: the Henry Hudson Bridge, Triborough Bridge, and the Manhattan Bridge in New York; Edward Henry Harriman's Arden House in Harriman, N.Y.; the Alfred I. Dupont mansion in Roslyn, N.Y.; the David A. Reed house in Washington, D.C.; the reconstruction of the Grand Army Plaza in New York City; the Memorial Amphitheater for Arlington National Cemetery; and various bicentennial buildings for Yale University. Of note are drawings of the grounds, details of buildings, and furniture for the New York Public Library, 1908-1909.

Photographs of buildings and of architectural drawings of buildings, residences, schools, clubs, and other projects (undated and circa 1910s-1920s), designed by Jacobs, many of which are located in New York City.