Answer by taking a quote from the following article:

Merman was born in her maternal grandmother's house located at 359 4th Avenue in Astoria, Queens in New York City in 1908, though she would later emphatically insist that it was actually 1912. Her father, Edward Zimmermann (1879-1977), was an accountant with James H. Dunham & Company, a Manhattan wholesale dry-goods company, and her mother, Agnes (Gardner) Zimmermann (1883-1974), was a teacher. Edward Zimmermann had been raised in the Dutch Reformed Church and his wife was Presbyterian.

Merman was married and divorced four times. Her first marriage, in 1940, was to theatrical agent William Smith. They were divorced in 1941. Later that same year, Merman married newspaper executive Robert Levitt. The couple had two children: Ethel (July 20, 1942 - 1965) and Robert, Jr. (born August 11, 1945) Merman and Levitt were divorced in 1952. In March 1953, Merman married Robert Six, the president of Continental Airlines. They separated in December 1959 and were divorced in 1960.  Merman's fourth and final marriage was to actor Ernest Borgnine. They were married in Beverly Hills on June 27, 1964. They separated on August 7 and Borgnine filed for divorce on October 21. Merman filed a cross-complaint shortly thereafter charging Borgnine with extreme cruelty. She was granted a divorce on November 18, 1964. Borgnine later told fellow actor Frank Wilson that he spent most of his short marriage arguing with Merman. By the end, he recounted how she came back from a film one day and said, "The director said I looked sensational. He said I had the face of a 20-year-old, and the body and legs of a 30-year-old!" Borgnine replied, "Did he say anything about your old cunt?" "No," replied Merman, "he didn't mention you at all."  In a radio interview, she said of her many marriages: "We all make mistakes. That's why they put rubbers on pencils, and that's what I did. I made a few lulus!" In her autobiography Merman (1978), the chapter entitled "My Marriage to Ernest Borgnine" consists of one blank page.  Ethel Levitt, her daughter, died on August 23, 1967, of a drug overdose that was ruled accidental. Her son Robert, Jr. was married to actress Barbara Colby who was, while estranged from Robert, shot and killed along with her boyfriend in a parking garage in Los Angeles in July 1975 by apparent gang members who had no clear motive.

Who did she marry first?
Her first marriage, in 1940, was to theatrical agent William Smith.