Georgia O'Keeffe’s surname was O'Keeffe from birth; she did not change it after marriage.
She was born Georgia Totto O'Keeffe, and O'Keeffe was her family name. The middle name Totto came from her maternal grandfather, George Victor Totto. Because she married Alfred Stieglitz in 1924, some biographies and casual references mistakenly lead readers to expect that she adopted his surname.
O'Keeffe continued to use her own name professionally throughout the marriage and afterward. This was consistent with her strong artistic independence and with the way her work was presented in exhibitions, books, and criticism.
Her name is also sometimes written without the apostrophe in informal contexts, but the standard form is O'Keeffe. The name is now strongly associated with American modernism, especially her large-scale flower paintings, New Mexico landscapes, and abstract compositions.