In 1891 Boring and Tilton left McKim, Mead, and White to form their own architectural partnership. Among their notable works were the Casino in Belle Haven, Connecticut (1891) and the Hotel Colorado in the resort town of Glenwood Springs, Colorado (1891). The partnership's work culminated in the 1897 design for the new federal Immigration Station at Ellis Island. This work was honored with a gold medal for Architecture at the Exposition Universelle, Paris (1900); a gold medal at the Pan-American Exposition, Buffalo (1901); and a silver medal at the Louisiana Purchase Exposition, St. Louis (1904). The partnership of Boring & Tilton ended in 1904. The men started working independently of one another but continued to share offices and equipment until 1915. In 1913, Boring was elected into the National Academy of Design as an Associate member.
In 1916, Boring joined the faculty of the Columbia School of Architecture, where he eventually became Director in 1919 and Dean from 1931 to 1932. As dean of architecture at Columbia Boring, and especially his successor Joseph Hudnut, encouraged the then-nascent modernism and incorporated studies in town planning.