Birch married Mary C. Rand in Minneapolis, Minnesota on June 24, 1916. His best man was longtime friend, Henry O. Havemeyer. He and his wife had two children whom they named Stephen and Mary. The Havemeyers sold their mansion and 730 acres of their estate to Birch and the York Room was added to the mansion for his daughter Mary and her husband in the 1920s. He lived in the mansion with his family until he died at age 68 at Doctors Hospital on December 29, 1940. "Birch is buried at Ferncliff Mausoleum in Hartsdale, New York. A stained glass window depicting Alaskan mountain scenery adorns this mausoleum."