Allen crafted the small and popular Beaux-Arts style bronzes, medical models for Harvard using the "lost wax" process, memorial tablets, portrait busts, portrait reliefs, "imaginative" pieces, garden fountains and life and death masques, as well as large memorials and architectural installations. His best-known large work is the pediment and statues atop the Supreme Courthouse in Manhattan. His sculptures are included in the collections of Boston's Museum of Fine Arts, the Metropolitan Museum, the Farnsworth Art Museum in Rockland Maine, the Concord Art Association, and the Smithsonian American Art Museum in DC. His own favorite piece, the heroic size Egyptian Head, was displayed in the New York World's Fair in 1939.