She married Harold Fowler McCormick (May 2, 1872 -), a son of Chicago's mechanical reaper inventor Cyrus McCormick, in 1895. McCormick and her father had an often stormy relationship, where her extravagance would often conflict with his known frugality.
The married couple spent their first 2 years living in Council Bluffs, Iowa. They later moved to Chicago. Her country retreat, located directly on Lake Michigan in Lake Forest, Illinois, named Villa Turicum, was famous for its ostentatious scale, and extensive gardens.
A famous story about McCormick involves an evening in 1901 during a party. News arrived that McCormick's son, John Rockefeller McCormick, had died of scarlet fever. This was whispered to her at the dinner table; she proceeded to merely nod her head and allowed the party to continue without incident.
In her later years she was known for her eccentric behaviour. She practiced astrology and celebrated Christmas on December 15th. In 1923 she received some minor press for claiming to be the reincarnation of the wife of King Tutankhamen, whose tomb had just been explored and was a popular topic. She was quoted as saying, "I married King Tutankhamen when I was only sixteen years old. I was his first wife. Only the other day, while glancing through an illustrated paper, I saw a picture of a chair removed from the King's chamber. Like a flash I recognized that chair. I had sat in it many times. She followed up in Time magazine by stating "My interest in reincarnation is of many years' standing.
In 1919 McCormick donated land she had received from her father as a wedding gift to the Forest Preserve of Cook County, to be developed as a zoological garden, later to be developed as Chicago's Brookfield Zoo.
In 1930 she had a growth removed from her breast and subsequently died of cancer two years later.