Georgia O'Keeffe's birth surname was O'Keeffe.
She was born Georgia Totto O'Keeffe, and she retained the family surname throughout her professional life. The name came from her father, Francis Calyxtus O'Keeffe, whose family was of Irish descent. “Totto” was her middle name, not her surname.
O'Keeffe married photographer and gallery owner Alfred Stieglitz in 1924. The marriage connected her life with a major figure in American photography and modern-art exhibition, but her artistic identity remained centered on her own work. She is conventionally known by the surname O'Keeffe rather than by a married name.
Some references describe her as Georgia Totto O'Keeffe, which can make the middle name seem like part of a double surname. It was not: O'Keeffe was the family name she used at birth and as an artist.