Cromwell's first wife was automotive company heiress Delphine Ione Dodge, the only daughter of Horace Dodge of Grosse Pointe, Michigan, one of the two co-founders of the Dodge Motor Company. They were married from June 17, 1920, until their divorce on September 28, 1928, and had one daughter, Christine Cromwell, in 1922.
On February 13, 1935, Cromwell married Doris Duke.[2] Both supported Franklin Roosevelt and his New Deal. He published books to present his economic ideas and advocated tighter control of the Federal Reserve.[1] In 1940, for 142 days,[3] he was the United States Ambassador to Canada. He resigned to enter the election for U.S. Senator from New Jersey, a race he lost to incumbent Senator William Warren Barbour.[4] After bitter and protracted legal proceedings Cromwell and Duke divorced on December 21, 1943. They had a daughter Arden Cromwell born July 11, 1940 who died a day later.
Cromwell was married to his third wife, Maxine MacFetridge, from April 24, 1948,[5] until her death on July 7, 1968.[6] Their daughter, Maxine Hope Cromwell (later Hopkins[7]), was born in New York on November 17, 1948.[8] Germaine Benjamin was Cromwell's fourth and last wife, from September 27, 1971, until her death in December 1986.[1]