William Gillett Ritch (May 4, 1830 – September 14, 1904) was an American public administrator, newspaper publisher, and Republican politician. He was appointed Secretary of the New Mexico Territory by President Ulysses S. Grant in 1873, and briefly served as acting governor of the New Mexico Territory in the summer of 1875. Before relocating to New Mexico, he previously served one year in the Wisconsin State Senate, representing Winnebago County. In historical documents, his name is frequently abbreviated as W. G. Ritch, and his last name is sometimes misspelled as Rich.