Douglas practised on his own until 1884, when his son, Colin, became ill. He then took Daniel Porter Fordham into partnership and practised as Douglas & Fordham. Fordham was born around 1846 and had been an assistant in Douglas's office since at least 1872. In 1898, having developed consumption, Fordham retired from the practice and went to live in Bournemouth where he died the following year. He was replaced as partner by Charles Howard Minshull, who had been born in Chester in 1858 and who became articled to Douglas in 1874; the practice became Douglas & Minshull. During the first decade of the 20th century, Douglas became less active but, for reasons which are unknown, the partnership was dissolved in 1909. The practice returned to the title of John Douglas, Architect. Minshull went into partnership with E. J. Muspratt in Foregate Street, Chester. When Douglas died, this partnership worked from the Abbey Square address as Douglas, Minshull & Muspratt.