Alfred Stieglitz's gallery 291 was located in Manhattan.
The gallery was at 291 Fifth Avenue in New York City, which supplied its famous abbreviated name. Stieglitz first called it the Little Galleries of the Photo-Secession, but it became widely known as 291. The space played a significant role in introducing European modern art and innovative American photography to U.S. audiences.
O'Keeffe's work was shown there beginning in 1916, after Stieglitz received photographs of her charcoal drawings. The gallery's exhibitions helped establish her as an important young modernist before she became best known for flowers, bones, and New Mexico landscapes.
Manhattan was a borough of New York City long before the city's current cultural institutions developed. The gallery's address was on Fifth Avenue in Manhattan, not in Brooklyn, Queens, or the Bronx. The number 291 refers to the street address rather than an exhibition number or a year.